* Idle Air Control (IAC) Valve: This is the most common suspect. The IAC valve regulates the amount of air entering the engine at idle. A dirty, faulty, or stuck IAC valve prevents the engine from getting the correct air/fuel mixture at low RPMs, leading to rough idling or stalling. Cleaning it (with carb cleaner) is often a simple first step, but replacement might be necessary.
* Throttle Position Sensor (TPS): This sensor tells the computer the throttle's position. A faulty TPS provides incorrect data, leading to poor fuel delivery at idle. A malfunctioning TPS often causes rough idling or stalling.
* Mass Airflow Sensor (MAF) Sensor: The MAF sensor measures the amount of air entering the engine. A dirty or faulty MAF sensor can cause a lean air/fuel mixture, resulting in rough idling or stalling. Cleaning it (carefully, following instructions) is often the first step; replacement is sometimes necessary.
* Vacuum Leaks: Small vacuum leaks can disrupt the air/fuel mixture, especially at idle when the engine is less powerful. Check all vacuum hoses and connections for cracks or disconnections. Pay close attention to the hoses connected to the brake booster, PCV valve, and intake manifold.
* Fuel Delivery Issues: While less likely if the engine starts, a problem with the fuel pump, fuel filter, or fuel injectors could contribute. A weak fuel pump might provide enough fuel for starting but not enough for sustained idling.
* Spark Plugs and Wires: While less likely to cause *only* an idling issue, worn spark plugs or faulty ignition wires can cause misfires, especially at low RPMs, contributing to rough idling.
* Computer (PCM/ECM): In rare cases, a faulty Engine Control Module (ECM or PCM) can cause erratic idling. This is usually diagnosed last, after other components are ruled out.
Troubleshooting Steps:
1. Check for vacuum leaks: Listen carefully near the intake manifold and vacuum hoses with the engine running. You might hear a hissing sound indicating a leak. Use a propane torch (carefully!) to check for vacuum leaks; if the engine RPMs change when the propane is near a leak, that's the culprit.
2. Clean the IAC valve: This is a quick and easy step. Disconnect the IAC valve and clean it thoroughly with carb cleaner. Let it dry completely before reconnecting.
3. Clean the MAF sensor: Use MAF sensor cleaner (not regular carb cleaner) and carefully clean the sensor element. Avoid touching the sensor element with your fingers.
4. Check spark plugs and wires: Inspect the spark plugs for wear and the wires for damage. Replace as needed.
5. Inspect the TPS: Testing the TPS requires a multimeter and knowledge of its operational parameters. A faulty TPS often needs replacement.
6. Check fuel pressure: A fuel pressure gauge will be needed to verify fuel system health. If the pressure is low, suspect the fuel pump or filter.
If you're not comfortable performing these steps yourself, take your S10 to a qualified mechanic. They have the tools and experience to properly diagnose and repair the issue. Providing the mechanic with the information you've observed (starts, runs, won't idle, sounds like choke) will help them focus their diagnostic efforts.
