If your 1990 LeSabre's idle speed is too high or too low, the problem likely lies elsewhere. Here's a more systematic approach to troubleshooting:
1. Check for Vacuum Leaks: Vacuum leaks are a common cause of erratic idle. Carefully inspect all vacuum lines for cracks, loose connections, or missing components. Pay close attention to the lines connected to the intake manifold, brake booster, and other vacuum-operated devices.
2. Clean the Throttle Body: A dirty throttle body can cause idle problems. Use a throttle body cleaner (following the instructions carefully) to clean the throttle plate and the surrounding area. Make sure you disconnect the battery negative terminal before doing this.
3. Inspect the Idle Air Control (IAC) Valve: The IAC valve regulates air flow at idle. It might be dirty or sticking. Cleaning it (often involves removing it and carefully cleaning it with a throttle body cleaner) might solve the issue. Replacing it is also a possibility if cleaning doesn't work.
4. Check the PCV Valve: A clogged PCV (Positive Crankcase Ventilation) valve can also affect the idle. Replace it if it's faulty.
5. Inspect the Throttle Position Sensor (TPS): A malfunctioning TPS can send inaccurate signals to the ECM, leading to idle problems. This sensor often needs professional testing or replacement.
6. Check the Mass Air Flow (MAF) Sensor: A dirty or faulty MAF sensor can also lead to idle issues. Cleaning it (carefully, following instructions) or replacing it may be necessary.
7. Diagnostic Trouble Codes (DTCs): Use an OBD-I scanner (specifically one compatible with your 1990 Buick LeSabre's system) to read any diagnostic trouble codes stored in the ECM. These codes can pinpoint the source of the problem.
Important Considerations:
* Professional Help: If you're not comfortable working on your car's engine, it's best to take it to a qualified mechanic. Improperly diagnosing or repairing these systems can cause further damage.
* OBD-I System: Remember that 1990 cars use OBD-I, which is significantly different from the OBD-II systems used in later vehicles. You'll need a scanner compatible with the OBD-I system of your Buick.
Instead of trying to adjust the idle speed directly, focus on identifying and fixing the underlying problem causing the idle to be off. Addressing the root cause will be far more effective and prevent further complications.
