To adjust the idle, you need to diagnose *why* it's incorrect. A fast or slow idle is a symptom, not the problem. Potential causes include:
* Vacuum Leaks: Check all vacuum hoses for cracks, leaks, or loose connections. A small leak can significantly affect idle. Pay close attention to hoses connected to the intake manifold and the brake booster.
* Throttle Body: The throttle body may be dirty or have a sticking throttle plate. Clean it thoroughly with throttle body cleaner, following the instructions carefully. Ensure the throttle plate moves freely.
* IAC (Idle Air Control) Valve: This valve regulates air entering the engine at idle. It's electrically controlled by the ECM. A dirty or malfunctioning IAC valve is a common cause of idle problems. Cleaning it might help, but it might need replacement.
* TPS (Throttle Position Sensor): A faulty TPS can send incorrect signals to the ECM, leading to an incorrect idle. It needs to be tested with a multimeter or a scanner.
* MAF Sensor (or Air Flow Sensor): A dirty or faulty MAF sensor can also affect idle. It should be cleaned carefully (with MAF sensor cleaner only) or replaced if necessary.
* ECM Issues: In rare cases, the ECM itself could be faulty. This is less likely but should be considered if other components are ruled out.
* PCV Valve: A clogged PCV valve can affect vacuum and cause idle issues.
How to approach troubleshooting:
1. Visual Inspection: Start by thoroughly inspecting all vacuum lines and the throttle body for visible problems.
2. Clean Throttle Body and IAC Valve: This is the easiest and often most effective first step.
3. Check for Vacuum Leaks: Use a vacuum gauge or your ear to listen for hissing sounds around vacuum lines. A spray bottle with soapy water can help locate leaks.
4. Diagnostic Scanner: The best approach is to use a code reader or OBD1 scanner (you'll need an adapter for your OBD1 system). This can reveal trouble codes stored in the ECM, which will point you towards the specific problem.
5. Professional Mechanic: If you're not comfortable working on your vehicle's fuel injection system, it's best to take it to a qualified mechanic. Incorrectly adjusting the system can cause damage.
There is no direct idle adjustment screw to turn; instead, you must address the underlying cause of the idle problem. Ignoring this and simply trying to "force" a different idle speed will likely mask a larger, potentially damaging issue.
