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Why Does My Car Stall?

Updated on February 20, 2017
A car engine can stall for numerous reasons.
A car engine can stall for numerous reasons. | Source

A car stalls for one of many reasons.

You could be dealing with a clogged fuel filter, a faulty fuel pump, dirty or faulty fuel injectors; or problems with a throttle position sensor, camshaft sensor, spark plug, or ignition coil; or problems with many other components.

Just looking at a list of every single possible part or fault is scary; you wouldn't know where to start. Trying to find the culprit without even a simple plan makes your problem harder and expensive to solve. You can spend a lot of money swapping components hoping it'll fix the problem.

This guide helps you think about potential clues even before you start checking components, gives you tips, and tells you how to go about diagnosing the suspect part(s) to verify your diagnosis so that you can repair the fault.

To help you with that, The next three sections discuss the three most common conditions under which your car is likely to stall. Then, each section lists the typical components involved under that condition, ordered from the most to the less likely. This way, you can go straight to the section that more closely describes the symptoms in your particular case.

First, a few important suggestions to keep in mind while you go over any particular section:

  • Pay special importance to the maintenance schedule for your particular vehicle make and model. You can find the schedule in the repair manual for your vehicle. There's a good reason for this: Most engine related problems--including stalling--can be traced back to a component or system in need of attention (think about those components or systems you have neglected or forgot to service).
  • Think about some maintenance task or repair project that you've recently done that may have triggered the fault. Did you unplug or disconnect something you forgot to replace? Did you install the correct part?
  • Have you checked your computer for trouble codes? Just because you don't see the Check Engine Light (CEL) come on, doesn't mean that your computer can't help you. See the Getting Help From Your Car Computer section below for more information.
  • Have your vehicle repair manual on hand. It'll save you time and money during this diagnostic, and for many maintenance and repair projects in the future. You can buy an inexpensive aftermarket copy at most auto part stores or online.

Keep these suggestions in mind while scanning the next three sections for the potential components causing the fault.

Index
I. My Engine Stalls When Idling or During Acceleration
II. My Engine Stalls When Warmed Up
III. My Engine Stalls Intermittently or While on the Road
IV. Getting Help From Your Car Computer
Fuel system problems are a common cause of engine stalls.
Fuel system problems are a common cause of engine stalls. | Source

I. My Engine Stalls When Idling or During Acceleration

An engine can stall while idling (either cold or warmed up) or while accelerating. Such a pattern may point to a problem in the fuel or emission systems. Here, you'll find the most common components or faults that can be causing you trouble.

1. Fuel System. A fuel filter prevents foreign particles like rust, dirt and water from entering the fuel system where they can do damage over time. But, a fuel filter will clog after miles of work.

First, you may find your engine losing power at highway speeds and possibly stalling. Then you'll notice a rough idle. Soon, the engine begins to stall at idle.

Usually, you want to replace the fuel filter every year or two. Check your car owner's manual or repair manual.

Besides a fuel filter, a bad fuel pump or fuel pressure regulator can show some of these symptoms. Fuel may flow appropriately at idle, but the engine will stall as soon as demand for fuel increases. Consult your repair manual to troubleshoot the fuel system, if necessary.

2. Air Filter. Just like a fuel filter, the filter in the air cleaner system is designed to trap dust and dirt particles and other foreign matter to prevent them from entering the intake manifold and combustion chambers where they would wreak havoc with the cylinders.

Over time, the paper element in the filter clogs and blocks proper airflow into the engine. This will cause the engine to idle rough and stall, or stall as you try to accelerate.

If you haven't replaced the air filter in more than two years, replace it. Most car manufacturers recommend replacing the filter every year.

3. Mass Airflow (MAF) Sensor. This sensor (aka Airflow Meter) measures the density (amount) of the air entering the intake manifold and reports to the car computer. The computer uses this signal to adjust the air-fuel mixture.

The sensor has an internal element that is exposed to incoming air, and thus to dirt and other particles that stick to it. When enough dirt covers the sensing element, it'll prevent the sensor from working and will cause the engine to stall.

You can easily remove the dirt using mass airflow sensor or electronics cleaner spray. Still, another possibility is that you are dealing with a faulty sensor.

4. Throttle Body. This issue is not as common as the previous ones but eventually happens if you fail to pay attention to the fuel system. Carbon buildup inside the throttle body, around the throttle plate or valve, will interfere with its operation. The engine may run rough at idle and stall.

You can fix this by removing buildup using carburetor cleaner. Spray cleaner on a clean shop rag, and use the rag to clean the throttle, around and underneath the valve.

5. Idle Air Control (IAC) Solenoid: Just like the throttle body, carbon buildup can also interfere with the proper operation of the IAC solenoid. The computer uses this valve to control airflow during engine idle and to regulate idle speed.

As with the throttle body, buildup accumulates over time in the passages of the IAC valve and can cause the engine to stall during idle. But a bad IAC valve can produce the same symptoms.

You can fix the problem by unplugging the IAC solenoid, removing it from the engine, and using carburetor cleaner to remove buildup form passages on the mounting surface. Be careful not to spray carburetor cleaner on the valve electronic components, though.

If you need to troubleshoot the sensor, consult your vehicle repair manual.

6. Positive Crankshaft Ventilation (PCV) Valve: On some vehicle models, a stuck PCV valve can cause the engine to stall.

If the valve sticks open, too much air will reach the intake manifold and cause the engine to stall during idle or acceleration.

The valve is usually easy to check. Remove the valve and shake it with your hand. If it doesn't rattle, the valve is likely stuck. On some models, the valve is a solid piece and will not rattle. You can remove gunk from inside a PCV valve with carburetor cleaner, but the valve is cheap and you can readily replace it in a minute or two.

7. Engine Coolant Temperature (ECT) Sensor: This is another electrical device that can cause you engine to stall at idle.

Your car computer uses information from the ECT to enrich or lean the air/fuel mixture. But the coolant sensor can fail after miles of operation. A common sensor electrical failure is an open or short in the circuit.

If the sensor circuit suffers an open, the computer will think the engine has reached operating temperature, lean the mixture, and cause the engine to idle rough and possibly stall.

The ECT sensor is used on most electronic fuel injected models, along with (usually) an air temperature (AT) sensor as well. The same issues apply to the AT sensor. So check both if you suspect a coolant temperature sensor. Consult your repair manual.

8. Exhaust Gas Recirculation (EGR) Valve. The EGR valve allows exhaust gases to recirculate through the intake manifold and into the combustion chambers. This helps reduce engine temperature and harmful oxides of nitrogen (NOx) emissions.

Most EGR valves are operated through engine vacuum or electronically, and only open after the engine has reached operating temperature and during acceleration

When an EGR valve fails and sticks open, you'll notice the engine running rough at idle and stalling. It is possible to check the EGR valve at home. Consult your car repair manual, if necessary.

9. Manifold Absolute Pressure (MAP) Sensor: This sensor measures atmospheric pressure. The car computer uses this information to control engine fuel needs.

If the MAP sensor sends the wrong information to the computer, it may cause the engine to stall. Check the electrical connection, rubber hose and wires when troubleshooting the sensor. See your repair manual for more information.

10. Vacuum Leak: A leaking vacuum hose, intake manifold or throttle gasket can also rob the engine of needed air and make it stall.

Depending on its size, a vacuum leak may not be a problem while your engine idles, but may cause the engine to stall during acceleration or at highway speeds, when the engine's demand for air increases.

II. My Engine Stalls When Warmed Up

A failed camshaft position sensor can cause the engine to stall.
A failed camshaft position sensor can cause the engine to stall. | Source

Temperature and electrical circuit problems can also combine to cause your engine to stall. This usually happens when one or more electrical or electronic circuits in a component open and brake electrical flow.

The component may function properly while the car is warming up. But once temperature rises, it causes wires in the circuit to expand. The broken wire disconnects, the device turns off and the engine stalls.

This is a common problem on devices exposed to high temperatures like the ignition control module, ignition coil, and even the crankshaft (CKP) or camshaft position sensor (CMP).

It can also happen to an electrical fuel pump. Although fuel helps cool the fuel pump during operation, if you often drive your vehicle with a tank low in fuel it can cause the pump circuitry to heat and fail.

You can suspect one of these devices if your engine stalls, starts again after the temperature drops, and stalls again once the temperature rises again.

III. My Engine Stalls Intermittently or While on the Road

Worn-out ignition system components can cause the engine to stall.
Worn-out ignition system components can cause the engine to stall. | Source

One of the hardest diagnostics to do is to locate a fault that is causing your engine to die intermittently. Yet, you can try checking a handful of components that may commonly cause this problem after having logged miles of work.

1. Distributor Cap, Spark Plug Wires, Spark Plugs, and Distributor Components. These components form part of the ignition system. Cap, wires and spark plugs should be checked and replaced at your manufacturer's suggested intervals. Consult your repair manual to check and troubleshoot these components.

  • Carbon traces can cause the distributor cap to fail. Remove and examine the top and underneath the cap, look for lines or carbon or even cracks on the cap.
  • Watch out for worn out or leaky spark plug wires. Worn out or leaky wires will interfere with current flow, causing the engine to stall intermittently, specially on rainy days.
  • Fouled spark plugs from oil or fuel and those with damaged electrodes or insulation will prevent the spark from reaching the ground electrode. Also, as a spark plug wears, the gap between the electrodes widens, making it hard for the spark to jump. Remove and examine the plugs. Clean the plugs, if necessary, and check their gap with a wire feeler gauge. If you recently installed new spark plugs, double-check their gap. Some new spark plugs come with the manufacturer recommended gap for each particular application, but it's a good idea to double-check. Also, check once more that you bought the right spark plugs for your particular engine. Your car owner's manual or repair manual have the recommended spark plugs for your model and the correct gap for the plugs.
  • Failures in other internal distributor components are not as common, but they do happen and may cause the engine to stall as well. Consult your repair manual.

2. Camshaft Position (CMP) Sensor: The computer uses this signal to make several adjustments, including spark timing and fuel.

Depending on your particular vehicle make and model, a failing camshaft sensor may cause the engine to stall intermittently, lose power, accelerate poorly, surge, start with difficulty, or misfire. Check your repair manual for the proper way to test your CMP.

3. Throttle Position Sensor (TPS): The TPS tracks throttle position and sends the signal to the car computer. The computer uses the signal to adjust engine timing and increase engine efficiency.

When the TPS goes out of adjustment or wears out, it can cause the engine to stall intermittently. Depending on your particular TPS and fault, you may need to adjust it or replace it.

4. Neutral Safety Switch and Ignition Switch: Any of these switches can suffer an open or wear out and cause the engine to stall intermittently. Consult your repair manual for testing or replacing the switches.

5. Battery Cable: A similar intermittent stalling problem can be caused by a bad battery cable.

Car batteries use large-gauge cables composed of several strands. If several of those strands break, they will interrupt electrical flow every time the vehicle travels over road imperfections, causing the engine to stall. Carefully check along the length of each battery cable for damage, corrosion and strands condition at each end where they join the terminals. A quick check is to start the engine and wiggle each wire to see if they cause the engine to stall.

You car computer can give important diagnostic clues.
You car computer can give important diagnostic clues. | Source

IV. Getting Help From Your Car Computer

The newer your vehicle model, the more components there are that may cause your engine to stall if the right conditions are present. Yet, a modern car computer can be of great help, including with many of those components mentioned in the previous sections.

If the Check Engine Light (CEL) is lit on your dashboard, it means a trouble code has been set in the computer memory. But you don't need to wait for the CEL to come on. The computer may have pending codes you don't know about that can give you some direction about where to start troubleshooting.

If you don't have a scan tool, take your car to a local auto parts store. Many of them will scan your car computer and let you know of any stored codes.

When retrieving one or more trouble codes, visually inspect and troubleshoot those components indicated by the codes and, if necessary, the circuits involved.

Remember, though, that a car computer can only tell you what system or component is involved in a potential failure; it can't tell you if a specific component or circuit has failed. A related component not present in the trouble code may be at fault. So it is important to test components and circuits before making any replacements.

The following video shows you how a worn-out vacuum hose is causing an engine to stall at idle. A regular inspection at home can help you catch this and other potential faults.

When your car stalls, it can happen for one or several reasons. And each one can happen under different conditions. That's why it's important to pay attention to the clues your own engine gives you: Does the engine stall when idling, as you accelerate, after it warms up? Here, you found some of the most common reasons for an engine to stall. So pay attention to the hints your engine gives you. Remember to make a visual inspection of any suspect component--or components--and troubleshoot before making a final decision. And don't forget your computer. The vehicle repair manual for your particular make and model should be of great help here.

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