Instead of trying to directly adjust the idle, you should focus on troubleshooting *why* the idle speed is incorrect. A problem with the idle speed could indicate a larger underlying issue. Here are some common causes and how to address them:
* Clean the Throttle Body: A dirty throttle body can significantly affect idle. Use throttle body cleaner and carefully clean the throttle plate and surrounding areas. Make sure to disconnect the battery negative terminal before doing this.
* Check the IAC (Idle Air Control) Valve: The IAC valve regulates air entering the engine at idle. A dirty or faulty IAC valve is a very common cause of irregular idle. It may need cleaning (with throttle body cleaner) or replacement.
* Check the PCV (Positive Crankcase Ventilation) Valve: A clogged PCV valve can lead to vacuum leaks, affecting idle. Replace it if necessary.
* Check for Vacuum Leaks: Vacuum leaks are a significant problem. Inspect all vacuum hoses for cracks, splits, or disconnections. Pay close attention to the hoses connected to the brake booster, intake manifold and the engine vacuum ports.
* Check the TPS (Throttle Position Sensor): A malfunctioning TPS sensor can provide inaccurate information to the ECM. This sensor may need cleaning or replacement.
* Check the MAP (Manifold Absolute Pressure) Sensor: Similar to the TPS, a bad MAP sensor provides incorrect information to the ECM. It too may need cleaning or replacement.
* Inspect the Air Filter: A clogged air filter restricts airflow and can affect idle. Replace if dirty.
If you've checked all these and the idle is still incorrect:
* Have the ECM scanned for trouble codes: An OBD-I scanner (for your year) can reveal any stored trouble codes that might pinpoint the problem. This is the most important step.
* Seek professional help: If you're not comfortable working on your vehicle's engine, take it to a qualified mechanic. Attempting repairs without proper knowledge can cause further damage.
In short, don't look for a screw to turn. Focus on diagnosing and fixing the underlying issue causing the incorrect idle speed. A systematic approach, starting with the simplest checks (cleaning the throttle body and checking for vacuum leaks) is the best way to proceed.
