* Idle Air Control (IAC) Valve: This valve regulates the amount of air entering the engine at idle. A dirty, faulty, or sticking IAC valve is a very common cause of this problem. It might need cleaning (with carb cleaner, following proper procedure) or replacement.
* Throttle Position Sensor (TPS): This sensor tells the computer the position of the throttle plate. A faulty TPS can give the computer incorrect information, leading to poor idle control. It may need cleaning or replacement.
* Mass Airflow Sensor (MAF) Sensor: This sensor measures the amount of air entering the engine. A dirty or faulty MAF sensor can cause a lean condition, leading to stalling at idle. Cleaning (with MAF sensor cleaner ONLY - avoid anything else!) is worth trying first. A failing sensor requires replacement.
* Vacuum Leaks: A leak in the intake manifold, vacuum hoses, or PCV system can disrupt the proper air/fuel mixture at idle, causing the engine to stall. Inspect all vacuum hoses carefully for cracks, holes, or loose connections.
* Fuel System Issues (Less Likely, but possible): While less probable given your description, a weak fuel pump or clogged fuel filter could contribute to insufficient fuel at idle.
* Dirty Throttle Body: A buildup of grime and deposits in the throttle body can interfere with smooth operation and idle. Cleaning the throttle body is often a good preventative maintenance step even if not directly causing the problem.
Troubleshooting Steps:
1. Check for Vacuum Leaks: Visually inspect all vacuum hoses and connections. Listen for hissing sounds near the intake manifold when the engine is running. A spray bottle with carb cleaner (carefully!) can help pinpoint leaks; if the engine RPM changes when sprayed near a leak, you've found the culprit.
2. Clean the IAC Valve and Throttle Body: This is usually the easiest and cheapest first step. There are many online tutorials showing how to do this correctly for your specific engine. Use appropriate cleaners (carb cleaner for the throttle body and IAC valve).
3. Clean the MAF Sensor: If the throttle body and IAC are clean and the issue persists, carefully clean the MAF sensor with MAF sensor cleaner. Be extremely gentle; do not touch the sensor element.
4. Check the TPS: This often requires a multimeter and a bit more technical knowledge. You'll need to check the voltage output of the sensor at various throttle positions. A faulty TPS often shows erratic or incorrect readings.
5. Consider a Fuel Pressure Test: If the other steps don't resolve the issue, a fuel pressure test might be necessary to rule out fuel system problems.
Important Notes:
* Safety First: Always disconnect the negative battery terminal before working on any electrical components.
* Professional Help: If you're not comfortable performing these checks or repairs yourself, take your Bonneville to a qualified mechanic. Misdiagnosis or incorrect repairs can cause further damage.
* Year Specific Information: Your 1993 Bonneville's specific engine (e.g., 3.8L V6, 3.1L V6, etc.) can influence which components are most likely to be at fault and how to access them for testing and repair. Consult a repair manual specific to your vehicle for detailed diagrams and procedures.
Start with the easiest and cheapest steps (checking for vacuum leaks and cleaning the IAC valve and throttle body). If the problem persists, progressively move to the more involved diagnostics. Good luck!
