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Why Your Car Stalls at Stops and How to Fix It

Dan Ferrell writes about do-it-yourself car maintenance and repair. He has certifications in automation and control technology.

A car that breaks at stops can eventually leave you stranded.

A car that breaks at stops can eventually leave you stranded.

If your car stalls at stops, you may be dealing with one or more potential faults:

  • Bad idle air control solenoid
  • Problems with a mass air flow sensor
  • EGR system leaks
  • Vacuum leaks
  • Fuel system issues
  • Ignition problems

Some problems are more common than others. The next sections touch on the most common sources of trouble and can save you time, help you diagnose the problem and, hopefully, fix it soon.

Index

1. Faulty Idle Air Control (IAC) Solenoid

2. Vacuum Leaks

3. Engine Stops When Idling Cold

4. Mass Air Flow (MAF) Sensor Issues

5. Fuel System Problems

6. Bad Ignition Coils

7. Faulty EGR Valve

8. Catalytic Converter Issues

9. Automatic Transmission Problems

10. Checking for Technical Service Bulletins (TSB)

Clean the throttle body and idle air control valve passages, if necessary.

Clean the throttle body and idle air control valve passages, if necessary.

1. Faulty Idle Air Control (IAC) Solenoid

The idle air control valve or solenoid is located on the throttle body. Your car computer uses the IAC to bypass the throttle valve to allow more air at idle.

A common problem with the IAC valve is buildup of carbon, fuel varnish or dirt inside the valve or throttle passages. Without enough air during idle, the engine stalls.

If the IAC motor has failed and stuck close, you'll see the same symptoms. You can troubleshoot the IAC solenoid at home, if necessary.

Check for intake gasket leaks or other vacuum leaks.

Check for intake gasket leaks or other vacuum leaks.

2. Vacuum Leaks

Vacuum leaks are a common cause of rough idling, stalling, and other engine performance issues. Specially, engines equipped with a mass air flow (MAF) sensor are prone to stall when idling with a vacuum leak.

A vacuum leak may come from:

  • PCV valve stuck open
  • Brake booster faulty hose or valve
  • Bad intake manifold gasket
  • Faulty throttle body gasket
  • EGR valve, gasket or hose
  • Loose or torn air duct between the MAF sensor and throttle body

Sometimes, the check engine light will come on and the computer may store trouble codes P0171, P0174 or P0300. You may also notice a misfire.

Vacuum hoses wear out over time and cause trouble on a sensor operation, like the one shown in the next video. So check all vacuum hoses for wear and damage, including those connected to the different sensors in your engine.

If necessary, this other post can help you find a vacuum leak in your vehicle.

Faulty Vacuum Hose Causing Trouble at Idle

3. Engine Stops When Idling Cold

Usually, when the engine stalls while idling cold, a sensor is behind the fault. You may want to check the following sensors or components:

Make sure to check for diagnostic trouble codes. Even if your check engine light is not on, there could be a pending code that can help you find the source of the problem.

Check for a clogged air filter or a leak in the air cleaner assembly.

Check for a clogged air filter or a leak in the air cleaner assembly.

4. Mass Air Flow (MAF) Sensor Issues

MAF sensors often become contaminated with dirt and fail to send the correct air flow volume data to the computer.

A problem with this sensor may trigger the check engine light. You can troubleshoot the MAF sensor at home using a digital multimeter. Often, all you need is clean the sensing element using mass airflow sensor cleaner.

When checking the sensor, verify that there are no air leaks in the air ducts between the sensor and throttle body. Confirm the air cleaner hoses and ducts are properly connected. Unmetered air entering the engine will also lean the air fuel mixture, causing the engine to stall at idle or while coming to a stop.

A faulty or worn fuel pump or some other component in the fuel delivery system can cause the engine to stall at stops.

A faulty or worn fuel pump or some other component in the fuel delivery system can cause the engine to stall at stops.

5. Fuel System Problems

Faulty components in the fuel system can also lead to this type of problem. For example:

  • Worn or faulty fuel pump
  • Clogging fuel filter
  • Bad fuel pressure regulator

Usually, a clogging fuel filter will give you the first signs of trouble when driving at highway speeds. Your vehicle may lack power because the amount of fuel is not adequate. Eventually, the filter will block fuel and starve the engine at idle.

If you haven't replaced the fuel filter at the recommended intervals suggested by the manufacturer (consult your car owner's manual or vehicle repair manual), replace the filter.

Just as a clogging fuel filter, a worn fuel pump may not be able to maintain the adequate pressure the system requires. If too little fuel is reaching the injectors, the engine may not be able to operate properly and die during idle.

A faulty fuel pressure regulator can leak fuel as well and cut out the engine at idle.

If you suspect a problem in the fuel system, don't replace components unless you run some tests or it's necessary.

You can get a relatively inexpensive repair manual for your particular model from Amazon. Haynes manuals come with step-by-step procedures for many troubleshooting, maintenance and parts replacement projects you can do at home.

Ignition system problems, like a faulty ignition coil or module, can cause trouble as well.

Ignition system problems, like a faulty ignition coil or module, can cause trouble as well.

6. Bad Ignition Coils

Modern vehicle models have incorporated several ignition coils to provide the spark each cylinder needs for combustion. Some models use one coil for every two cylinders, while other use one coil per cylinder.

On this models, a bad ignition coil may cause a misfire, but may not cause the engine to stall. However, if the engine is unable to maintain the correct idle speed because a fault is affecting more than one coil, it may stall at idle.

If you've noticed misfires along with a stalling-at-idle condition, check the ignition coils.

Carbon buildup inside the EGR valve and intake manifold passages can prevent the EGR form closing.

Carbon buildup inside the EGR valve and intake manifold passages can prevent the EGR form closing.

7. Faulty EGR Valve

Common problems with the exhaust gas recirculation (EGR) system are a stuck EGR valve, vacuum leaks or an electrical circuit fault.

Carbon buildup tends to accumulate around the valve and intake ports. This may block the flow of exhaust gases to the intake, but it can also prevent the valve from closing, allowing a continuous flow or exhaust gases into the cylinder.

If the EGR valve sticks open, you'll notice a rough idle, possibly misfires and stalling.

Other symptoms of an EGR valve stuck open may include:

  • Rough idle at a stop light
  • Check engine light on
  • Fuel odor during engine operation
  • Increase fuel consumption

If you haven't checked the valve for proper operation or carbon buildup, this is a good time to test the EGR valve and remove buildup, if necessary.

On some models, a fault in the EGR system may trigger a trouble code. Scan your computer memory for codes, even if you don't see the check engine light on. If you don't have a scan tool, your local auto parts store may download codes for you.

A clogged catalytic converter or muffler can cause your vehicle to stall at stops.

A clogged catalytic converter or muffler can cause your vehicle to stall at stops.

8. Catalytic Converter Issues

Miles of service and engine performance issues like misfires can eventually take its toll on the catalytic converter and cause your vehicle to stall while idling or coming to a stop.

A catalytic converter may become plugged or the substrate may disintegrate. This will increase exhaust backpressure and may or may not trigger the check engine light. Also, depending on your particular problem, you may become aware of these other symptoms:

  • Rattling sound underneath the vehicle
  • Low engine power
  • Smell of rotten eggs

There are some converter tests you can do at home if you suspect a problem with it. Or your can have the catalytic converter checked at the shop, if necessary.

Keep in mind that a restricted muffler may show the same symptoms.

Check your automatic transmission fluid level and condition.

Check your automatic transmission fluid level and condition.

9. Automatic Transmission Problems

Problems with the automatic transmission can also cause your vehicle to stall at idle. This is usually because of:

  • Low transmission fluid, affecting torque converter operation.
  • Torque converter problems
  • Plugged transmission cooler system

If your particular transmission has a converter clutch, you may notice the engine stalls when shifting into reverse. This is usually caused by a clogged oil cooler or cooler line.

10. Checking for Technical Service Bulletins (TSB)

Problems in a particular engine system can also lead to a stall-at-idle condition. For example, some 2004-05 Chevy Malibu vehicles with the 2.2L engine were experiencing hesitation, stalling at idle with the engine warmed, and other driveability issues. The problem seems to be a voltage spike coming from a cooling fan that is affecting the ignition system.

Some vehicle models leave the factory with these type of problems and are reported to car dealers through technical service bulletins (TSB).

These bulletins can also help you with problems that you may not be aware of until you bring your vehicle to the shop.

Thus, a TSB can reveal problems with your particular vehicle and help you solve an issue that otherwise might be difficult or costly to find out about later on.

How to find TSBs for your vehicle:

You can also gain access to TSBs for your particular vehicle through the NHTSA website. Just follow the instructions provided in this PDF document.

Other websites can also help you find these bulletins. Using a major search engine, search for the term technical service bulletin.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

© 2019 Dan Ferrell

Comments

K R PAI on November 01, 2019:

I find this pictorial narration extremely useful Thanks for sharing

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