Dan Ferrell writes about do-it-yourself car maintenance and repair. He has certifications in automation and control technology.
Symptoms of a Bad MAF Sensor
Bad MAF sensor symptoms can vary, depending on the vehicle make and model:
- rough idle
- erratic performance
- stalling when transmission is put in gear
- trouble codes P0171, P0174
- hard starting
- poor acceleration
What Does the MAF Sensor Do?
The MAF sensor measures air volume and density as it makes its way into the intake manifold. The electronic control module (ECM or car computer) uses these and other sensors’ inputs to deliver the right amount of fuel to the engine. This is why you can get all kinds of performance issues when your MAF sensor isn’t working right.
Why Clean Your MAF Sensor?
Although MAF sensor issues can vary, a common problem is dirt or debris finding its way into the sensor housing. Foreign matter can eventually cover the MAF’s sensing elements like the hot wire, interfering with its operation.
Cleaning the MAF sensor is a simple procedure. Often, this is all you need to fix a rough idle and other engine performance issues.
So, if you suspect a dirty MAF sensor, or you are getting a MAF-sensor-related trouble code like P0171 or P0174, try the following procedure. In most cases, all you need is a Phillips screwdriver and a can of MAF sensor cleaner to do the job.
1. Where the MAF Sensor Is Located
2. How to Clean a MAF Sensor
3. Preventing MAF Sensor Issues
1. Where Is the MAF Sensor Located?
Look for the MAF sensor between the air filter box and the throttle body. On some models, the sensor is inside the air filter housing.
If you need help locating the sensor, get the vehicle repair manual for your particular vehicle make and model.
You can get a relatively cheap copy through Amazon. Haynes manuals come with step-by-step procedures for troubleshooting, parts replacement, and maintenance projects you can do at home. So, you’ll recoup your small investment pretty soon.
2. How to Clean an MAF Sensor
Before your start, here are a few notes you need to be aware of:
- Some manufacturers recommend replacing the MAF sensor rather than cleaning it, if the hot wire or sensing elements are dirty, because cleaning the wires won’t restore the sensor to its original efficiency. However, cleaning a dirty MAF sensor may work just fine most of the time.
- If your sensor has logged around 100,000 miles or more, though, you might want to consider a new replacement, especially if engine performance seems a bit sluggish after cleaning the sensor.
- Manufacturers recommend NOT using MAF sensor cleaner on the Karman-Vortex type MAF sensors used on some Lexus, Toyota, and Mitsubishi models and other imported vehicles. Consult your car repair manual, if necessary.
Now, if you are ready to start, make sure the ignition switch is in the Off position. Then set the parking brakes and pop the hood.
- Unplug the MAF sensor electrical connector. Be careful. You may need to depress a plastic tab or lock in order to release the connector.
- Unscrew the bolts, usually two, that hold the sensor in place. On some models, the sensor is located inside the air filter box. Consult your vehicle repair manual, if necessary.
- Remove the sensor from the air intake boot assembly or air filter box.
- Check the rubber gasket that seals the MAF sensor to its housing. If damaged, replace it.
- Make a visual inspection of the sensor. Check the sensor’s hot and, if equipped, cold wires, for signs of dust, dirt, debris or bugs.
- Place the MAF sensor on a workbench or similar surface, and let it rest on a shop rag. The rag will help you catch cleaning solution runoff as you spray the sensor.
- Put on your goggles and latex gloves.
- Clean the sensor by spraying cleaning solution on it. Follow the instructions that come with your product. Whatever you do, though, avoid touching the sensing wires. They are fragile and can easily break.
If the hot and cold wires are covered with dirt or debris, you can use a camel-hair artist's brush to wipe them clean.
- Spray a small amount of the sensor cleaner solution into a small, clean cup.
- Soak the small brush in the cleaning solution.
- Use the brush to wipe dirt and debris from the wire(s).
- After cleaning the MAF sensor, allow it to dry completely for a few minutes.
- In the meantime, remove dust and debris from the air filter housing and air ducts. If there’s dirt or debris in the ducts, than the assembly is leaking air past the air filter.
- Seat the air filter properly and seal the air filter box and ductwork.
- Install the MAF sensor, make sure the rubber seal sits correctly, and secure the sensor with the mounting bolts.
- Plug back in the MAF sensor electrical connector. Make sure the tab locks in place.
- Erase the trouble codes, if necessary, using a scan tool.
- Start the engine and listen to the engine idle.
Depending on your particular model and trouble codes set in the computer’s diagnostic memory, you may have to drive a few miles before engine performance improves. For example, you still may notice a rough idle. The ECM may need some time to adjust to the new input parameters from the cleaned sensor.
If cleaning the sensor didn’t solve your engine performance issues, and you suspect problems with the sensor, you may want to test the MAF sensor.
A couple of recommendations:
- If you found dirt or debris attached to the wires or sensing elements, this may be an indication of a faulty self-cleaning circuit. You may want to check the “burn off” relay and, if necessary, the circuit. Consult your vehicle repair manual.
- Some manufacturers recommend replacing your air filter after cleaning the MAF sensor.
3. Preventing MAF Sensor Issues
For the most part, the MAF sensor in your car will work reliably without giving you any problems. It’s when you need to replace the air filter or remove the air cleaner assembly for maintenance or repair tasks, or when you forget to maintain the air cleaner assembly, that you may see MAF sensor operation issues. So here are a few pointers you may want to keep in mind:
- Whenever you encounter problems with the MAF sensor, closely inspect the intake boot and air filter box for tears, damage or loose connections that might allow air to bypass the MAF sensor.
- When cleaning the MAF sensor or replacing the air filter, make sure the boot is properly set. Secure the boot to the air filter box and throttle body with the clamps without leaving any air gaps.
- If air gets to the throttle plate without being measured first by the MAF sensor, your engine will run lean and you’ll end up with engine performance issues again.
- Replace the air filter at your manufacturer suggested intervals, and keep the air filter box and air cleaner assembly properly sealed. This helps prevent MAF sensor contamination issues.
- If you frequently drive under dusty conditions, you may want to clean the MAF sensor more often, for example every 50,000 miles or sooner, and replace the air filter more often.
The follwoing video gives you a quick take about the MAF sensor location, how it works and how to clean it.
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.
© 2019 Dan Ferrell
Dan Ferrell (author) on August 27, 2020:
A bad MAF sensor won't make a car noisy. Probably water caused some internal damage if it found its way into the cylinders. You may be hearing a damaged piston, connecting rod or bearing. You may be able to diagnose the problem. This other post can help:
The MAF code is a separate issue you need to diagnose. Hope this helps.
Craig on August 27, 2020:
I drove through a deep puddle and my car stalled. After I got it running again my car was making a tot of noise. Car was fine before this. Now my car is making less noise but still some. Almost sounds like a knocking but when I do a test on it. It comes up as my mass air flow sensor. Would this make my car sound like that
Benefit Chrisy Machwa on December 10, 2019:
Dan Ferrell (author) on October 28, 2019:
The MAF sensor is a good start. You also may want to check other parts as well like the air filter (clogged),
restricted PCV valve or hose,
and engine coolant temperature sensor (ECT)
Anita on October 27, 2019:
Thank you for posting all this...Very kind of you and I'm hopefully going to check everything that applies to my vehicle. Have been having worsening revving and accelerating issues only during cold season.
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