1. Idle Air Control (IAC) Valve: This valve regulates the amount of air entering the engine at idle. A dirty or faulty IAC valve is a very common cause of this problem.
* Troubleshooting: Try cleaning the IAC valve with carburetor cleaner. This often involves removing it, spraying it thoroughly, and letting it dry completely before reinstalling. If cleaning doesn't solve it, replacement is likely needed.
2. Throttle Position Sensor (TPS): This sensor tells the computer the throttle's position. A faulty TPS can cause erratic idling and stalling.
* Troubleshooting: This usually requires a multimeter to check the voltage output at various throttle positions. A bad reading indicates a faulty TPS needing replacement. Many auto parts stores can test your TPS if you remove it.
3. Mass Airflow Sensor (MAF) Sensor: This sensor measures the amount of air entering the engine. A dirty or faulty MAF sensor can lead to poor idle and stalling.
* Troubleshooting: Carefully clean the MAF sensor with MAF sensor cleaner (never use anything else, like brake cleaner). Avoid touching the sensor element. If cleaning doesn't help, replacement is likely necessary.
4. Vacuum Leaks: Small leaks in vacuum hoses can disrupt the engine's idle.
* Troubleshooting: Carefully inspect all vacuum hoses for cracks, holes, or loose connections. Replace any damaged hoses. Use a vacuum gauge to check for significant vacuum leaks.
5. Fuel Delivery Problems: Issues with the fuel pump, fuel filter, or fuel injectors can starve the engine of fuel, causing stalling, especially at idle.
* Troubleshooting: Check fuel pressure using a fuel pressure gauge. A low reading indicates a problem with the fuel pump, filter, or regulator. A clogged fuel filter is a relatively easy and inexpensive fix. Faulty injectors are harder to diagnose and often require professional attention.
6. PCV Valve: A clogged positive crankcase ventilation (PCV) valve can cause a vacuum leak and affect idle.
* Troubleshooting: Replace the PCV valve; they're inexpensive and relatively easy to access.
7. Engine Coolant Temperature Sensor (ECT): A faulty ECT sensor can provide incorrect information to the engine computer, affecting the fuel mixture and idle.
* Troubleshooting: This usually requires a multimeter to check for correct resistance readings at different temperatures.
8. Distributor (if applicable): Older vehicles might have a distributor. Worn points or a faulty ignition module can cause intermittent stalling.
9. Computer/ECU Problems: Although less likely, a problem with the engine control unit (ECU) is possible. This usually requires professional diagnosis.
Troubleshooting Steps (in recommended order):
1. Check for obvious vacuum leaks. This is the easiest and quickest check.
2. Clean the IAC valve. This is a cheap and relatively easy fix that often solves the problem.
3. Clean the MAF sensor. Make sure to use the correct MAF cleaner.
4. Check fuel pressure. This will rule out fuel delivery problems.
5. Replace the PCV valve. A cheap and easy preventative step.
6. Inspect and replace any visibly damaged vacuum hoses.
7. Test/replace TPS and ECT sensor These require a multimeter.
Important Note: If you are uncomfortable working on your car, take it to a qualified mechanic. Improperly diagnosing and repairing these issues could lead to further damage. Always disconnect the negative battery terminal before performing any electrical work.
