Dan Ferrell writes about do-it-yourself car maintenance and repair. He has certifications in automation and control technology.
Signs of a Bad PCV Valve
You probably don't realize how important the PCV system—the Positive Crankcase Ventilation (PCV) valve and its related components—is to the well-being of your engine.
In this article, we will discuss how car owners can test their own PCV valves. Before we get to that, here's this article in a nutshell:
- What happens when the PCV valve fails,
- what the PCV valve does, and
- how to test it.
PCV Valve Function in a Nutshell
What the PCV valve does:
• Uses the engine vacuum to pull blow-by gases out of the crankcase.
• Pushes the gases down the intake manifold and back into the combustion chambers where they are re-burned.
Some signs it's failing:
• One or more oil seals or gaskets fail.
• The engine surges.
• The engine may produce black smoke.
• Internal engine pressure increases.
• Moisture and sludge build up inside the engine.
How to test it:
• Inspect rubber parts.
• Replace mesh filter beneath valve.
• Disconnect hoses and carefully inspect them.
• Remove valve and shake. If it does not rattle, it needs to be replaced.
What Happens When a PCV Valve Fails?
Symptoms of a Stuck Closed PCV Valve or System
A bad PCV valve or related component can produce a number of symptoms. For example, if the valve clogs, or gets stuck in the closed position, you'll notice one of these symptoms.
- Increase in internal engine pressure
- Failure of one or more oil seals or gaskets
- Engine oil leaks
- Low whistling or moaning noise
- Moisture and sludge buildup inside the engine
- Engine surges
- MAF sensor trouble code
- P0171 or P0174 trouble codes
- 02 sensor trouble codes
Symptoms of a Stuck Open PCV Valve
If the PCV valve gets stuck open, or a system hose gets disconnected or ruptured—producing a vacuum leak—you'll notice one or more of these symptoms.
- Engine misfires at idle
- Lean air-fuel mixture
- Presence of engine oil in PCV valve or hose
- Increased oil consumption
- Hard engine start
- Rough engine idle
- Possibly black smoke
- Oil fouled spark plugs
A PCV valve stuck open can trigger the "check engine" light due to increased airflow. A diagnostic computer may erroneously blame this light on a mass airflow sensor or oxygen sensor instead, making it harder for you to detect the real source of the problem.
What Does a PCV Valve Do?
First, let's discuss the valve's function so that you understand better the reasons behind the symptoms. Understanding this will help you make better sense of the system when you inspect and test it.
The History and Function of the PCV Valve
Up until the late 1950s, car engines released "blow-by" gases—unburned fuel—to prevent engine damage. Problem was, these gases were harming the environment. Really badly.
When your car engine is running, an air-fuel mixture enters each cylinder. Hundreds of powerful explosions take place to release the fuel's energy, producing highly toxic and harmful gases. After each combustion process, the exhaust valve routes these gases into the exhaust system where the catalytic converter turns them into much less toxic fumes before releasing them into the atmosphere.
Still, a small quantity of the gas in the combustion chambers finds its way into the crankcase (engine block) by way of pressure leakage between the piston rings and the cylinder wall.
Left on their own, these vapors and fumes will play havoc with your engine. Blow-by gases contain hydrocarbons (unburned fuel), carbon monoxide (partially burned fuel), particulates, water, sulfur, and acid. Together, these substances will corrode any engine metal component they touch, dilute engine oil, build up harmful sludge that accelerates parts wear, and plug small passages and hoses.
In 1961, the PCV system was introduced to deal with this problem. This simple emission control system uses the engine's vacuum to pull blow-by gases out of the crankcase, pushing them down the intake manifold and back into the combustion chambers where they are reburned.
Yet, the PCV system will fail with poor system or engine maintenance.
Why the PCV Valve Is Important
Bad PCV valves can cause engine oil contamination, sludge build-up, oil leaks, high fuel consumption, and other engine-damaging problems, depending on the type of failure.
Although you can detect some of these problems before they escalate with simple inspections, a failure of the PCV valve or related components often results in expensive repairs. That's because most car owners don't include the PCV system in their maintenance routine. Even though some car manufacturers suggest replacing the valve at regular intervals, car owners still forget to replace it. To add to the problem, not all manufacturers stress the importance of regular system inspections.
How to Test Your PCV Valve
Unfortunately, many car manufactures are not strict about PCV system maintenance. Some suggest servicing the system every 20,000 or 50,000 miles. However, a more frequent system inspection helps prevent costly repairs and keep the engine running smoothly.
1. Locate the PCV Valve
To start checking the PCV system in your vehicle, first, locate the PCV valve and its related components. Depending on your particular model, you may find the valve on a rubber grommet on the valve cover; on a breather opening around the intake manifold; or to one side of the engine block.
Keep in mind that some new models don't have a PCV valve at all; instead, you'll find a simple vacuum hose going from the valve cover to an air inlet duct. Others may have a simple restrictor in place. Still, you can check the restrictor, hoses, and other components.
If you are not familiar with the PCV system in your vehicle, or can't find the valve, buy the service manual for your particular vehicle make and model from a local auto parts store. The aftermarket manual costs around $20, and it contains instructions for many simple maintenance tasks and repairs. If you don't want to buy a copy right now, check the reference section of your local public library for the manual, or your library's website for access to an online shop manual.
2. Check the PCV Valve System
Luckily, once you locate the valve, it doesn't take much to check the system.
- Check PCV system parts. Rubber components like grommets, O-rings, and hoses swell and turn hard and brittle after constant exposure to high temperatures. They begin to leak. Replace one or more of these components as necessary.
- Carefully disconnect the valve and any system hoses and visually inspect them. If you find the hoses filled with slime, clean them with PCV solvent or lacquer thinner and replace the valve. Or, simply replace those components along with the PCV valve.
- Many engine models use a simple, inexpensive valve, and many car owners just replace it every service interval. Other valves incorporate heating elements and cost more. Regardless of the type of PCV valve your engine uses, always buy a quality brand valve, since it's more likely to have a more precise calibration for your specific engine model.
- On some engines, you'll find a mesh filter underneath the valve. Some car manufacturers recommend replacing the filter every 30,000 miles or so.
- Most PCV valves contain a spring-loaded device. Once you remove the valve, shake it with your hand. You'll hear a rattle. If you don't, it is time to replace the valve. Even if the valve rattles, if your engine is experiencing one or more of the bad PCV valve symptoms described above, it's a good idea to replace the valve.
- If your PCV valve is electrically heated, check the heater coil using an ohmmeter. The coil should have some resistance. If resistance is infinite, the coil is open and the valve needs to be replaced. Consult your vehicle repair manual, if necessary.
Some vehicles—including some old Ford Escort models—come equipped with a small, hollow, plastic block with no moving parts. If you have this type of valve, just clean with lacquer thinner, if necessary, and reinstall.
3. Alternative Testing a PCV Valve During Engine Operation
Besides visually inspecting the condition of the different PCV valve-related components, test the system during engine operation. These tests can be especially helpful if your PCV valve is difficult to access or you are looking for further evidence that the PCV valve is the cause of your issue.
Ways to Test for Vacuum Using RPMs
- Start the engine and let it idle for about twenty minutes to warm it up to operating temperature.
- Then, open the hood and disconnect the valve from the valve cover and block the end of the valve with your finger. You'll feel a vacuum from the system sucking at your fingertip and notice a momentary idle speed drop of about 40 to 80 RPMs.
- Another way to test for vacuum is to pinch or block the vacuum hose connected to the PCV valve. Idle speed will drop between 40 to 80 RPMs and then rise back to normal. If not, look for a blocked or restricted vacuum hose or valve.
- If you notice a bigger rpm drop and the engine idle smooths out, your PCV valve might be stuck open.
- If you don't feel vacuum at your fingertip, check the valve and hoses for gunk obstructing airflow. Clean the PCV valve and hoses with lacquer thinner and a thin hose brush, if necessary.
Alternative Test (Without Using the PCV Valve)
- On some engines, access to the PCV valve is difficult. In these models, you can remove the engine oil dipstick and seal the dipstick tube opening with a piece of tape. With the engine at idle, remove the cap from the oil filler on the valve cover. Then place a thin piece of cardboard over the opening. Wait for about one minute. You'll notice vacuum suctioning and holding the paper against the opening. Otherwise, there's a leak in the system, or the system is clogged. Check the condition of the hoses, hose connections, and grommet.
4. Finding Moisture in the PCV Valve or System
Once you remove the PCV valve, you may find traces of a milky brown fluid in the PCV valve or hoses when examining the system. This doesn't necessarily mean there's a problem with the valve or PCV system. A milky substance usually means moisture in the oil.
The accumulation of moisture in the oil is usually caused by:
- frequent short trips (usually under 10 miles)
- a restricted fresh air flow in the PCV system
- coolant leaking into the engine
In the first case, you can solve the problem by replacing the engine oil more frequently; since short trips do not allow the engine and oil to reach operating temperature, moisture doesn't have a chance to vaporize and clear out.
If you drive your vehicle long distances frequently enough, usually over 20 minutes or more and at highway speeds, and find moisture in the system, then you may have a coolant leak issue. If you suspect a coolant issue, you may want to bring your car to the shop for a diagnostic.
Maintaining the PCV System
Sometimes, bad PCV valve symptoms are misrecorded as coming from a bad sensor. That's why it's important to check the PCV valve and related components regularly. This is especially true if you own a 2001 or older model, where the PCV system is not monitored by the OBD-II system, and won't illuminate the check engine light if something goes wrong.
It just takes a few minutes to check the system. However, if your engine lacks a PCV valve, or you can't reach it without removing one or more components, consult your workshop manual for the best way to check your particular system.
Also, check the service schedule for your PCV system and replace the valve at intervals even if it seems to be in good condition. Most PCV valves and related components are inexpensive and will save you money in costly repairs if you replace them at the suggested interval.
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.
Questions & Answers
Question: Could a bad PCV affect engine start?
Answer: It can certainly make it hard to start; if it sticks open it may lead to a no start.
Question: Will a bad PCV cause my truck to stall when running and accelerating?
Answer: If it sticks open it's possible.
Question: Is it true that if you suck on PCV valve and air comes in, it's defective?
Answer: Most are designed as a check valve to prevent the valve from flowing back, for example, during a back-fire.
Question: Can a bad PVC valve cause blue smoke to come out of my exhaust?
Answer: Yes it can.
Question: Should you be able to pass air flow in both directions in a PCV valve for testing purposes?
Answer: Usually, a PCV valve is normally closed when the engine is not running; as the engine accelerates, the valve opens to allow blowby gases. So you shouldn't be able to pass air flow in both directions. However, some models like the ‘87 Escort, use a fully open valve design.
Question: Could a bad PCV valve cause my car to use a lot of oil?
Answer: Check if the PCV valve is stuck and check for bad hoses.
Question: Will I have a faulty PCV valve if I have residue around oil cap? Its a 2009 Holden Commodore VE V6. Valve might be stuck & now has contaminated oil (since replaced). So now could be a seal or gasket problem.
Answer: If the PCV valve or a hose or the system was clogged, it can cause pressure to rise, leading to seal failure. Has the system diagnosed, if necessary, before sludge and moisture cause more damage?
Question: Would a bad PCV cause a dipstick to blow completely out of the oil tube?
Answer: If the PCV system is plugged, pressure in the crankcase will build and may cause a dipstick to blow.
Question: Does a PCV valve in a 2008 Jeep Wrangler unlimited with a 3.1 v6 flow in both directions?
Answer: I believe it flows in one direction since it needs to remove harmful blowby gases out of the crankcase.
Question: I have a 2004 Mazda MPV. The climate control heating doesn’t work in the front, but the rear heating does from the rear controls. Do you have any ideas?
Answer: There could be a problem with the heater control valve or the controls, not letting the valve opening all the way.
Question: Can a bad PCV valve cause braking problems? There is a vacuum hose on the brake booster.
Answer: The PCV won't cause braking problems. Check the valve and hose to the booster. Make sure they are well connected. This post may help:
Question: Would a bad valve cause a smell in the car, like an irritant that burns eyes and nose and such?
Answer: You might be getting oil fumes inside the cab. Check the valve and system for a restriction. Some valves connect to a breather filter. Check the filter and change it, if necessary. Hope this helps.
Question: How can it be the brake pads when the error codes came back Diagnosing Trouble Codes P0171 and P0174. Another code regarding the crankshaft? Also, a warning light that looks like a faucet came on, and the car almost stops on me. Is this trouble for a 2008 BMW 328I? Is it called the valve cover instead of PCV Valve?
Answer: The faucet-like warning light is the check engine light. You may have more than one problem going on. When the P0171-4 codes appear, it means the car's computer is unable to make proper adjustments to control the air-fuel mixture, thus the car almost stopped. Too much fuel is going through the engine. The PCV valve is different than the valve cover. The PCV valve most likely connects to the valve cover on the engine. The cover is on top of the engine and serves as a "lid" for the engine valves. In most engines, the engine oil fill cap is located on a valve cover.
Question: Where is the PCV valve on a 2010 Daihatsu Mira manual?
Answer: There could be two possible locations for this model. Look at the valve cover, passenger side, towards the firewall. There should be a hose that connects to the cover (1/2 an inch hose). The valve plugs into a grommet on the valve. Another possible location is under the throttle body. I believe is attached to two rubber hoses.
Question: Should I replace the hose if it is hard and not easy to squeeze?
Answer: Yes. Rubber hoses become hard and brittle from the high temperatures in the engine compartment. Eventually, they break and leak.
Question: Could a disconnected breather hose to a K&N air intake cause a rough idle and misfire with code #P0272?
Answer: It can lead to a misfire and rough idle, but the P0272 in general points to a cylinder number 4 misfire and cause a rough idle. You can check for the cylinder misfiring by unplugging one cylinder spark plug wire at a time, if possible.
Question: I have 2009 Honda Civic LX-S and I see oil around my PCV valve. What should I do?
Answer: First make sure there's a good connection; there could be too much internal pressure, or a problem with the seals or leaks. Go over the post, you'll get an idea about checking the valve, if necessary.
Question: Would a bad PCV Valve be a reason for errors when I fill up my tank and attempt to start my car? It does not start, but on the second attempt, if I pump my accelerator while turning the ignition it will start. But there would be a large white-grayish cloud from the exhaust.
Answer: There could be a problem in the evaporative control (EVAP) system. If there’s a leak in the system, fuel vapors may be pushed into the intake. Sometimes, removing the gas cap when trying to start the engine with a full or almost full tank may help. But have the system checked, if necessary.
Question: My 2007 Taurus has a heated PCV. What is the wire connection called?
Answer: That's a heated PCV valve. Some Vulcans came with it to prevent cold weather from freezing the valve.
Question: How often must I change my PCV valve?
Answer: You can check your PCV valve every few months. Change it if it's filled with sludge or if it's stuck.
Question: I am currently in the process of having blower motor wiring and PCV valve heater recall fixes done. It’s on a 2007 BMW 328xi Wagon. My valve cover gaskets are also leaking slightly? Are these related?
Answer: If the PCV system was clogged, it may have caused pressure to increase and the gaskets began to leak.
Question: Could faulty pcv valve cause blue smoke from exhaust only at idle ?
Answer: There could be a restriction in the PCV system creating pressure in the crankcase. This may push oil into the combustion chamber and burn the oil, which you'll see as blue smoke.
Question: Will a check engine light come on for a misfire?
Answer: The P0300 (random misfire) and the P030x series codes (specific-cylinder misfire codes) point to this type of issues.
Question: will a bad PCV valve cause my car to vibrate?
Answer: I don't think a bad PCV valve itself will cause the vibration, but it can lead to other issues that may cause the engine to vibrate. You may want to check this post:
Question: Would a PCV valve not working properly cause something like a high-pitched vacuum sound? Would it also be why I get "check gauges" warning in the dash?
Answer: Usually when you see the "Check Gauges" light, one or more of the gauges is indicating a system has gone out of its normal operating parameters.
This may be related to the sound you hear, maybe not. When this high-pitch (whistle) sounds comes with the engine cold, often on deceleration, it often points to an intake vacuum leak. It may disappear after the engine has warmed up. This could be a faulty gasket. The sound may come from the dipstick not fully seated, and the whistling sound will travel through the PCV system.
Check other vacuum hoses and gaskets, if necessary.
Question: Where is PCV valve located in a Chevrolet Beat 2013?
Answer: I don't have the manual, but I hope this video helps:
Question: Can an intake manifold be damaged by a faulty PCV valve?
Answer: If the valve fails, pressure can cause acid vapor through the breather element. It'll combine with the air-fuel in the intake; after some time you may see buildup.
Question: Can i clean a heated pcv valve?
Answer: You may be able to clean the valve if you don't damage the electrical circuit or heater. You may want to try electrical contact cleaner, if necessary.
Question: Does Toyota have a PCV valve?
Answer: Yes it does. If you need to find the PCV valve in your engine, you can search for it in Youtube. But buying the manual for your particular model is better. Check your local auto parts store or Amazon, online. Most likely you’ll be able to replace it yourself, if you need to change it.
Question: I have a 2008 Mini One 1.4 petrol. The engine idle is rough and there appear to be excessive exhaust fumes through the oil cap when removed, could this be due to a blocked PCV?
Answer: Check the PCV, breather and hoses in the system, make sure they're not clogged.
Question: Why do I have fuel coming from my PCV valve?
Answer: If you smell gasoline in the oil or fumes going through the valve, possibly the piston rings are too worn and letting fuel pass through. This may happen in a rich mixture condition.
Question: My Chevy Cruze 2010 1.6 is misfiring when the engine is getting warm and during acceleration. When stooping in traffic lights, it gets worst. It feels like the engine is throwing out. What could be the cause?
Answer: Take a look at this post. This may help you:
Question: What kind of damage can result from a bad PCV valve?
Answer: You'll see sludge buildup that will slowly destroy internal engine components, and oil leaks from damaged seals.
Question: Where is the pcv valve of Nissan Sunny 1991?
Answer: Look in one of the hoses that attach to the valve cover
Question: Can a bad PCV valve cause my 03 Ram 1500 5.7 Hemi to keep throwing a p0440 code? I've replaced all the EVAP systems and hoses but still, I keep getting this code. I've also changed the gas cap and nothing changed.
Answer: You have a leak somewhere. The PCV won't throw that code. Check the filler neck and fuel vapor pressure sensor.
Question: Can a stuck/closed PCV valve cause oil to leak into the intake manifold?
Answer: This is rare, but it may happen. Usually, oil leaks will get stuck in the air filter. As crankcase pressure builds with a stuck closed PCV valve, the oil may leak through seals and gaskets, oil travels up the clean air hose and to the air filter. If the oil passes through the filter, it may find its way to the intake.
Question: A PCV valve heater, what’s the difference in PCV valve and PCV valve heater?
Answer: Basically, the PCV system is used to draw fresh air into the crankcase through the air filter or a separate PCV breather filter. On some models, a heated PCV system is used to help warm the moisture (icy) contained in the vapors absorbed through the PCV valve in cold weather. It speeds up operation of the valve to prevent excess pressure buildup in the crankcase.
Question: I have a 2012 Beetle with that amount of oil and Volkswagen says I need a new PVC valve at a crazy price. Is it hard to replace a PVC valve?
Answer: It shouldn't be that difficult. This video gives you an idea about the replacement.
Question: Can a bad PCV valve cause bad vacuum at idle?
Answer: This other post may help:
Question: Can a bad PCV cause no vacuum in the crankcase?
Answer: A stuck PCV can reduce vacuum in the crankcase (actually pressure from blowby). Check also for leaking hoses in the PCV system. If you need to check the valve, this other post may help:
Question: I replaced a new crankcase on my vehicle but now there is a noise. What is it?
Answer: Carefully look under the car with the engine idling an take a look. Check what side of the engine the noise is coming from. You'll get an idea what's going on.
Question: Will a bad PCV valve cause a miss? Number 5 cylinder is not firing.
Answer: Yes, it is possible. Misfires are usually tricky to diagnose. If you got a trouble code pointing to cylinder #5, the job could be easier. Check for ignition coil, spark plug, wire, fuel injector as well.
Question: Where’s the POV valve on a Camry v6 2008?
Answer: This video might help you out:
Question: I have a 2017 Subaru Impreza, which has just bunny hopped violently, then blown a lot of smoke out the rear. My Subaru dealer has found the center is missing from the PCV Valve. A replacement part is on order. If that fixes the problem, what other issues could this have caused? Where could the missing center part have gone? And what further repairs/checks should I make sure are done if replacing the PCV valve fixes the issue? It is still under warranty.
Answer: Probably what you heard is the releasing of pressure building up in the crankcase, the lower part of the engine. This happens when the PCV valve or part of the system clogs. This type of fault is likely to blow oil seals. So make sure to keep an eye on the oil level and check the front and back of the engine for potential leaks if you see a drop in oil level. If you've never serviced the PCV system, it'll be a good idea to check the engine for sludge buildup. Internally, this is a very corrosive substance that can damage internal components.
Question: Will a bad PCV valve cause a rear main seal to leak oil?
Answer: If the valve or the system is obstructed, it'll increase pressure in the crankcase and eventually damage one or both seals.
Question: I have a 2008 BMW X5 3.0si. It doesn't Start and doesn't crank. What do you think it could be?
Answer: Make sure your battery is properly charged. Then check the starter system circuit and, if necessary, the starter motor itself. This other post can help you check the circuit:
Question: I have an Audi B7 1.8T. It has rough idle, no revs. Engine light and EPC diagnosis results show pedal or throttle body and airflow. Can a PCV valve cause this error?
Answer: The problem is more likely with the throttle body (carbon buildup [airflow obstruction? mechanical biding?), as the diagnostic revealed. The PCV only routes crankcase gases into the intake to reburn. It's possible the vehicle is in "limp mode", hence no revs.
Question: Is it possible to change 2005 Mazda Tribute v6 valve cover gaskets without disconnecting the battery?
Answer: It may be possible, but it’s better to play it safe. You can use a memory saver. Or make one with a 12V dry cell battery. Use a couple of jumper wires and an inline 5 amp fuse in the positive side. Connect ground to the engine and power to the alternator battery terminal. That way you’ll have more room to work if you need it.
Question: My 2009 Escalade dies when going down the road at 30-40 mph intermittently (once every 100-200 miles). It will restart immediately. Any ideas?
Answer: Intermittent faults are hard to diagnose, but these other two posts may help you here:
Also, make sure to download diagnostic trouble codes, even if the check engine light is not on. There may be a pending code that can guide you. If you notice the engine stalls only when reaching operating temperature, look for a faulty crankshaft, camshaft sensor, ignition module or fuel pump.
Question: Will a disconnected PCV valve cause my truck to misfire?
Answer: Yes, it's possible.
Dan Ferrell (author) on August 04, 2020:
This other post may help:
Swilson50 on August 02, 2020:
hey dan, thanks for sticking with me! i disconnected the vacuum hose between the pcv valve and the intake manifold and quickly covered it with the palm of my hand. i couldn't watch the rpms, but after a huge suck of air, the idle smoothed out once i blocked the hose. a little smoke came out of the pcv valve while i did this. since i've had the same pattern with 2 pcv valves, i'm moving on to a vacuum leak at the intake manifold. indy said the car passed a smoke test....would a smoke test identify a leak at or around the intake manifold? its a plastic manifold. how would i test for a leak at the manifold and its gasket? spray the area with MAF sensor cleaner?
btw, i had a brief CEL and stored codes for cylinder 1 and 3 misfires.
Dan Ferrell (author) on July 28, 2020:
Here are a couple of simple tests you can do that might help:
+ Bring the engine to operating temperature
+ Then pinch-block the PCV vacuum hose that goes to the valve
+ Normally, you should notice a momentary drop in idle of about 50 to 80 rpm and then, idle speed should correct itself. A greater drop in idle indicates a problem with the PCV valve.
Another possibility is an intake manifold gasket leak. This can also create an increase in vacuum inside the crankcase.
Swilson50 on July 28, 2020:
the clean air intake is not clogged. i put the 3 year old oem pcv valve back on. is it possible there is too much vacuum sucking out of the crankcase from the intake manifold? or the crankcase isn't sucking enough air from the air filter box (what could block the the flow of air into the crankcase? what else could it be?
Swilson50 on July 17, 2020:
ahhhh, the fresh air inlet.......very interesting. i disconnected it to swap the valve but didn't look at it any further. is there an easy way to test it? the intake hose comes from the engine side of the air box, but its not easy to access that end. i doubt i can disconnect this hose at the valve end without disconnecting the coils. thanks for responding so quickly!
Dan Ferrell (author) on July 15, 2020:
The two most common sources of negative crankcase pressure come from a restricted fresh air inlet or using the wrong PCV valve for the application. So heed your mechanic's advice and take it from there. Hope this helps.
Swilson50 on July 15, 2020:
Hi Dan, nice article! i have a 2011 Audi Q5. i've experience strong negative pressure in the crankcase (loud suction sound and engine almost stalls when removing dipstick cover). i don't see codes on my cheap scanner, but a mechanic said he saw misfire codes. the idle is rough (not varying RPM, just skipping sound...misfiring maybe). also, an intermittent strange warbling sound when accelerating slowly from standstill on a cold engine. there is some oil in the pcv valve. the valve was only 3 years old (replaced as part of the oil burning recall by audi), but i replaced it anyway with a crappy aftermarket part (mechanic scolded me and told me to go buy an oem part). possibly a little improvement with the aftermarket part, but not really better.
it sure sounds like the pcv is a problem, but is it possible that there is just too much vacuum from the engine and its overwhelming the pcv valve? what else can i look at?
i want to get your opinion before i go spend $220 for an oem part.
thanks in advance, Scott
Dan Ferrell (author) on June 25, 2020:
You can check the valve cover for leaks. If it is leaking then replace the gasket. Diagnose the overheating problem. This could fix the misfiring issue. These other posts may help:
Korie on June 25, 2020:
I have a 2000 cadillac deville and my car has been nisfiring and saying it is overheating the person i bought it from said i need to buy a valve cover gasket to fix the issue wvat do you think ?
Dan Ferrell (author) on April 30, 2020:
Here we're assuming the seal was installed properly and the leak is not coming from an oil cooler, gasket, oil pan or valve cover. From your description, it seems the PCV system is plugged, but a faulty vacuum line as well (possibly clogged), can cause carbon buildup that increase pressure and a failed seal. If you've noticed misfires, this could be another sign of a problem in the PCV circuit.
Another possibility is a damaged or scored crankshaft surface-sealing area. This may come from an exposed seal-spring (previous seal?). Your model is relatively new, but you mentioned you like to load it to transport lumber and large items. If the main bearings have worn out, possibly lack of proper lubrication (low oil level, dirty oil?), this could be shown in a leaking seal if the crankshaft has even a minimal chance of perpendicular (up and down) movement. Have the crank sealing area checked for signs of wear or damaged. Hope this helps.
Carole on April 29, 2020:
I have a 2012 Ford Escape 4x4 V6 with 56,000 miles on it – No major repairs (only 3rd brake light and lift gate glass hinges, repaired myself) but 6 months ago I noticed a trail of oil going up the driveway to where I parked my vehicle and a pool of oil underneath. There were no codes or warning lights and it was obvious that the main seal had to be replaced. I had it towed to the Ford Dealer and they replaced the main seal and PCV valve and it ran great as usual. This past Monday the same thing happened and they want to replace the main seal again but the mechanic that worked on it six months ago noted that the seal was puffy almost like it was pushed out by pressure and that’s why he changed the PCV valve as well six months ago. What are they missing here? Is there something else they are not seeing? Is there some kind of compression test that can be done on the crankcase to determine if there is a pressure problem that may in turn damage the engine – something that can be fixed to prevent a re-occurrence? They used the dye to find the leak but unless the work was not performed right the first time I can't imagine how the main seal could be gone again in six months time. I don’t want this to happen again. I love this vehicle - it’s a pleasure to drive and go mudding with. I bought it when they stopped making the Ranger; Since the rear seats fold down so well I can transport lumber and large items as I did with my Ranger. Any advice is much appreciated.
Dan Ferrell (author) on March 02, 2020:
You need to download the trouble codes from the computer memory and take it from there. If you don't have a scan tool, bring it to an auto parts store. Most will get the trouble codes for you. Hope this helps.
William Norva on March 02, 2020:
Hi Dan, my 1998 Dodge Dakota, V8 SLT 5.2L recently had an engine hesitation issues while traveling on a 35 mi low speed run and suddenly the engine light came on. I have not brought it to garage for them to look at it for diagnostic test. I acquire this truck in 2014 and only drive it only when I have to and from the VA hospital in North Las Vegas. I'm afraid to bring it to the shop for their high cost repair charges. Need your expert advice. I would like learn If I could do it myself. Thanks Navy Vet on a fixed income.
Dan Ferrell (author) on February 13, 2020:
I think what you are hearing is a cylinder relieving pressure through an oil control valve. System pressure is pushing on a valve, which makes that sound you hear. This is not an actual issue but probably the new valve you are using is helping to increase the sound. However, engine using too much oil it's an issue and can be related to the sound. You need to investigate where the oil is going. Check the coolant fluid color. A milky color would reveal an oil leak into the system. The oil could going through the exhaust system as well. This other post may help:
DXP on February 13, 2020:
HI I have 2014 Kia Sorento its using a lot of oil saw I just change the pvc valve.when I turn of the engine there is a puff sound coming from the engine. Can you tell me if that's the pcv valve that I just installed. It was not there before.What should I do now?
Dan Ferrell (author) on October 14, 2019:
If you drove the car for a few weeks with a clogged filter, probably it worn down the fuel pump. But there could be other reasons why your car stalls. This other post may help:
Dan Ferrell (author) on October 14, 2019:
This is a maintenance item. If the PVC valve is stuck, manufacturers recommend replacing it.
Summer on October 14, 2019:
How would I fix a stuck pcv valve and how would I know it is indeed stuck and not broke
Clarence on October 12, 2019:
I own 2003 nissan exterra. Supercharged v6. It started running rough I changed the fuel filter. Trash came out of old filter . It shuts of somtimes at stops. When going slow it dies at stop sign.
Dan Ferrell (author) on October 05, 2019:
Usually a busted PCV valve comes from a clogged system. Pressure increases and can damage seals and soon you got oil leaks. If the engine overheated and a hose or PCV valve was too close, it may have damaged the hose or valve.
Jonathan Sinex on October 05, 2019:
My pcv valve in my saturn is busted and spraying oil onto thermostast is that the reason for the overheating or is the reason for the busted hose because of the overheating in another area
Dan Ferrell (author) on September 28, 2019:
It seems combustion is failing in those cylinders. The flashing CEL is a warning, your catalytic converter may die if raw fuel keeps getting to the cat. The problem could be in the ignition system. Have the fault properly diagnosed. It could become an expensive fix later on. Hope this helps.
Malven on September 28, 2019:
I have a VW mk5 fsi. For the past 6 weeks each time i start my car in the morning the idling has changed and now rough with check light flashing and it idle rough till after driving and the temp is up. When its idling in neautral it will be shaking with 3 cylinders misfiring. When its in drive the shaking becomes less. Whenever i am driving only cylinder number 1 will be misfiring and no shaking but when i am at a stop sign or traffic lights the check light begins to flash and idle changes. Could it be the PCV?
Paul A on September 27, 2019:
Thanks Dan, much appreciated.
There are error codes, but I haven't checked since the failure...
How would the Camshaft play up? Surely if the cam was causing issues it would cause them and stay caused wouldn't it? I will look in to the Throttle control.
I'm thinking its time for a new engine. I've never in my life known 1 engine to have so many different faults, all at the same time!
Thanks again, Paul.
Dan Ferrell (author) on September 27, 2019:
It is possible the PCV valve is stuck open, causing a lean condition. But there could also be a problem with the throttle control as shown by the EPC light. Start by checking for trouble codes and see if there are any pending codes. If the camshaft is acting up, that may explain the symptoms as well.
Paul A on September 27, 2019:
Hi Dan, how are you?
I have an issue that I think is the PCV. Over the last few weeks I've had issues with intermittent stalling, usually when the revs are low & I'm still moving. I've had intermittent issues starting, in that it wouldn't start without giving it a few revs, which I initially thought it was related to stop start being on when I stopped & turned the engine off, but it then spluttered when I tried to start it even though the stop start had been off. Anyway, last night the engine started intermittently spluttering, just for moments, on and off for around 4 hours. Come to think of it, there have been several moments over recent weeks where its 'spluttered' and the EPC light came on, but was fine after stopping & starting... Back to last night; the time between splutters/noticable lack of power grew shorter and then, as I pulled in to a car park it coughed, tried to die, and then did. I managed to get it running again, with difficulty, and it ran like a bag of spanners, but did get a little better after a couple of minutes. If I reved it, there was a sweet spot between 2 & 3,000 revs where it sounded almost normal. On idle it sounded like it was running either on 3 cyclinders or missfiring on all 4. I checked the plugs & Coils & they're all fine (I have spares that I use for this). All 4 plugs were sooty & they appear to be running lean. I've had a cam sensor issue for a few weeks & we thought it was the change but the mechanic checked & thats fine... He did clear some build up out of the variable timing oil pressure thingamybob at the front & it ran so much better. He mentioned the oil gause was missing, but I can't see that being too much of an issue; I suspect that was removed when I had the chain changed around 3.5 years ago. Anyway... I can't think of anything else at the moment.
Dan Ferrell (author) on August 12, 2019:
Keep an eye on the coolant and oil level. White smoke upon starting the car first thing in the morning could mean oil leaking through a valve guide seal. But you can also have coolant leaking into a cylinder, causing the puff of smoke. Hope this helps.
Ernest on August 12, 2019:
Pls can u help me solve cold start smoke on my corolla pls
Dan Ferrell (author) on July 27, 2019:
If you want to know if the PCV system in your vehicle is working correctly, take it to a shop and have them do hook it up to an exhaust analyzer. Basically they need to check CO and O2 readings. If the system is working properly but you are noticing issues like oil sludge or dilution, there could be oil leaks. If you engine has high mileage, engine wear can be the source of the problem. Hope this helps.
Prince on July 26, 2019:
How a PCV system can be checked for correct operation
Dan Ferrell (author) on June 13, 2019:
It's probably a vacuum leak that was left when back the cover. Check for a vacuum hose or the gasket itself and make sure that everything was put back together right.
Darlene on June 13, 2019:
My car is making a high pitch noise still after i had a new vale. Asket cover replaced engin light is gone now
Dan Ferrell (author) on January 07, 2019:
This is usually caused by problems with an oxygen sensor, leaking exhaust manifold, retarded spark timing, leaking fuel injector, oil contamination, and misfires. To see reasons for high oil consumption, this other post may help:
Stephan on January 06, 2019:
Can bad PCV valve may cause following error: P0420 OBD-II Trouble Code: Catalyst System Efficiency Below Threshold (Bank 1) and consumption of 0.6 l oil per 1.000 km? Ford Fiesta, 1.4 16V, 2003.
Dan Ferrell (author) on September 26, 2018:
White smoke is usually associated with coolant. Check for coolant loss -- if there's a leak, there could be engine problems (cylinder head , gasket or block)
When I hold engine revs at about 1.5 thou revs I get clouds of whitish smoke out of axhaust.smells of fuel . Any ideas0 on September 26, 2018:
When i hold revs at about 1.5 thou revs i get clouds of whitish smoke from exhaust car is 1.8 v50 55 petrol
Dan Ferrell (author) on September 10, 2018:
This post might help you:
Roderick on September 10, 2018:
My car consumes excesive oil, and sometimes appears in display the message: stop!, oil pressure too low.
What do you think, maybe its the famous PCV valve?
I have an Audi A4 B8, 1800 cc.
Dan Ferrell (author) on July 20, 2018:
You may need a length of hose to try to locate the source of the sound. A hose may be loose or hanging back there. Follow the brake booster hose and see if it is properly connected. You may need a small mirror, something like a telescoping round mirror.
Robert on July 19, 2018:
I have a problem that sounds like the pcv valve my 95 mustang GT idles really rough & it has loss power & it surges & backfires from the intake I changed most of everything but still the same I can hear air coming from the back of the engine but I don't see exactly where it's coming from is the pcv located somewhere back there or is it any other hoses that run towards the back ??
Dan Ferrell (author) on May 24, 2018:
Hope it helps
Kiraro Yuuki on May 23, 2018:
Thank You so much, I haven't tested if it solved the oil smoking problem but because of this I decided to check it and found that the hose was loose, hope it solves the smoke!
Dan Ferrell (author) on April 13, 2018:
Get an estimate from a reputable shop and get a general idea of the condition of the engine - and take it from there. How much more are you going to need to invest in the car - major repairs. And see if it is worth keeping it.
Stunna yung on April 12, 2018:
And I just bought this bmw 645ci 2004 convertible with 133, miles no lights on the dash just smoke from occasion to occasion for nine thousand cash should I try an get my money back or keep and repair like the car just don’t to be out a lot of money fixing the car thank u
Stunna yung on April 12, 2018:
It only does it when I stop for a long period of time and when I turn my a/c on white/blue smoke still the same or something else thank u
Dan Ferrell (author) on April 12, 2018:
Usually blue-gray smoke is associated with oil burning in the combustion chambers. In a worn, high mileage engine this means worn rings or cylinders. Yours probably has some leaking valve stem seals or something similar. You might want to do a compression test or a vacuum gauge can even help- they are relatively cheap.
Stunna yung on April 12, 2018:
Hi please need help I have a 2004 bmw 645ci and when car is on and idle to right temperature I get white/blue smoke from tailpipe and if I turn a/c on I get big cloud of smoke what’s goin on here please help and thanks in Advance
Dan Ferrell (author) on March 31, 2018:
There could be a restriction in the intake manifold. Check the PCV hoses and valve as well.
Mike on March 30, 2018:
Having problem with rough idle when engine is on. If i remove the pcv valve from the valve cover and have the engine running at idle speed the idle works fine, but when i reinstall the pcv valve the rough idle comes back and black rich smoke comes out of tailpipe.
Dan Ferrell (author) on March 09, 2018:
Check it every few months, to prevent gunk from accumulating, along with the connecting hose and the other connection. Check it specially to prevent it gets stuck either open or close. If you notice gunk around the valve or hose replace it.
Nasir Khan on March 08, 2018:
In Corolla 95 Engine 4AE 1.6 EFI, when i change the PVC Valve?
Dan Ferrell (author) on March 05, 2018:
Look at the hose that attaches to the valve cover.
Khan on March 04, 2018:
Where is the pcv of Nissan Sunny b13 engine
Dan Ferrell (author) on October 16, 2017:
If the PCV system is clogged, it may build pressure in the crankcase and push seals to release pressure. Check the system.
Silva on October 14, 2017:
I recently replaced my 4L ford ranger rear main oil seal as i noticed some leaks coming between the engine block and transmission,and there was some sludge in the oil cap of the engine,but after some mile it started leaking again but a small amount,,,could this be the cause of the PCV valve?
Dan Ferrell (author) on September 20, 2017:
The way you describe the problem sounds like you had an oil leak somewhere, and the pressure made things blew up. On some models, the computer will cut off power if there's a loss of oil pressure to save your engine from self-destructing. You need to check where the leak originated. (was the valve properly installed?). There's where you'll find the problem.
Scott king on September 18, 2017:
I have a 2000 Toyota avalon.check engine light came on and it was a bad oil control valve.when heat is on u smell oil.I don't drive it hard ,change oil .well. tonight I was doing about 60,65 and all of a sudden it started smoking,lots of smoke.I went to pull over but now power .never ran hot never made any sounds.I had windows down and radio off.no ticking, nothing sounded like it broke and allot my antifreeze blew out with the oil.I would really appreciate it if you could give me your professional Thoughts of what might have happened and y..you really seem that you know what and y things happen
Dan Ferrell (author) on August 22, 2017:
If the valve or one of the connectors or hose, or pipe is leaking, most likely you'll get a misfire at idle. It'll be better to replace the valve, but make sure everything else is in good condition and properly connected.
Warren on August 22, 2017:
I accidently broke the PCV on my car,1989 toyota 4fa, stupidly though. I have glued it just to hold it in one piece, i have put it back. Now the car is misfiring. I also did a test by closing the vacuum pipe. Idling come slightly back to norm. Whistle nose from valve. Is the valve the problem.
Dan Ferrell (author) on June 14, 2017:
Thanks a lot for sharing. Glad to hear it's fixed,
Lauwrice Degamo on June 11, 2017:
just want to share,,
I finally solved the surging idle problem ( when engine is warm at operating temperature) of my 2008 corolla engine .
It was a leaking oil pump which cannot deliver the proper oil pressure to activate the VVT-i system. it had a P0016 code Crankshaft-camshaft correlation.
had to check the oil control valve, filter, timing chain, VVT then finally open the oil pump assembly which had internal damage which caused the leak.
hope this can help other DIY mechanics.
Dan Ferrell (author) on May 29, 2017:
Have you tried getting the valve loose. Rotate the valve with a pair of pliers, use penetrant oil if necessary. And carefully dislodge the valve with a small screwdriver.
Hope this helps
Dan Ferrell (author) on May 17, 2017:
Have you checked for coolant leaks? Does it smell like oil burning or an electrical wire burning?
You can try having an assistant starting the car for you while you watch under the hood where the smell is coming from. You may be dealing with a slipping belt that gains traction a few seconds after the engine starts.
You can also check the PVC valve yourself. Just remove it and shake it. It should rattle. if filled with gunk, clean the valve and any hoses, if necessary.
mike h on May 17, 2017:
my 2002 sport trac has a burning smell soon after you first crank it then it goes away. oil level is fine so it's not losing oil. friends say it's the pcv valve. not allowing oil to flow properly. any suggestions?
Dan Ferrell (author) on March 15, 2017:
Sometimes you can just blow through the hose to check for a blockage. I use a set of thin brushes to clean hoses and some types of valves. It works great in old Fords. If much of the roughenss is gone, you probably got it all clear. Check for codes once in a while and the proper maintenance. There's a lot of simple maintenance stuff you can do on your own and save you a lot.
Lauwrice Degamo on March 15, 2017:
yeah it's fine now, though there's a little roughness sometimes.
by the way my car is a 2008 corolla and has DBW. in the case of the breather hose system, could it be blocked somewhere in the valve cover ? causing an imbalance in the air flow inside the valve cover? pcv valve won't shut off in idle when there is not enough air intake in the breather hose? .
Greg on March 14, 2017:
Don't use lacquer thinner it's going to melt anything plastic the rubber diaphragm and probably the hoses
Dan Ferrell (author) on March 14, 2017:
Is the idle fine now? Also trace all the way the blowby gases have to follow from the valve cover back to the intake manifold. Make sure the passages are all clear. Another item you want to check is the idle air controlled (IAC) valve around the throttle body. The passages in this valve usually get filled with buildup and the engine begins to surge. And don't forget to scan for codes. Emission control sensors will usually trigger a code when something doesn't go right.
Lauwrice Degamo on March 12, 2017:
i have replaced the pcv valve,(also tried cleaning the valve) but still the engine is surging at idle.
i tried pulling the breather hose from the valve cover and the idle went fine. so i decided to put a breather filter in and blocked the breather hose form the air duct.
Dan Ferrell (author) on January 31, 2017:
Have you checked the valve? Some you can check; if it rattles, it is still good. Otherwise you may remove all the
gunk with carburetor cleaner. Most valves are pretty cheap, so you can replace it if you have to. Check the hoses and connections as well.
Lauwrice Degamo on January 30, 2017:
Having problem with surging idle when engine is warm. If i remove the pcv valve from the valve cover and have the engine running at idle speed the idle works fine, but when i reinstall the pcv valve the surging idle comes back.
Dan Ferrell (author) on December 07, 2016:
Yeah, they require some little maintenance once in a while, but it goes a long way. A bit of work or just replacing it as required can save your engine from demise. And it doesn't cost much.
Thanks for commenting.
donald on December 07, 2016:
my pcv valve was stoped up and it was pushing oil out pretty bad. put a new pcv valve in now its ok.203 chrysler town&country 3.8
Dan Ferrell (author) on September 20, 2016:
It seems to vary (model, engine, and hose size) and possibly wether you are connecting to manifold or ported.
Check to see if you can find those vacuum tees with the correct size for your application.
John C on September 13, 2016:
Can I route the hoses from each valve cover (one with pcs valve, one without) to a single vacuum port?