If your idle is running too high or too low, the problem likely lies elsewhere. Possible causes include:
* Dirty throttle body: Buildup of carbon deposits can interfere with smooth air intake and affect idle. Cleaning the throttle body is often the first step.
* Vacuum leaks: Cracks or holes in vacuum hoses can cause erratic idle. Inspect all vacuum lines carefully.
* Faulty Idle Air Control (IAC) valve: The IAC valve regulates airflow at idle. A malfunctioning IAC valve is a common cause of idle problems. These often need replacement.
* Failing throttle position sensor (TPS): The TPS informs the ECU of throttle position. A faulty sensor can lead to incorrect idle adjustments.
* Dirty air filter: A clogged air filter restricts airflow, potentially affecting idle. Replace if dirty.
* Problems with the ECU: In rarer cases, the ECU itself could be malfunctioning. This is usually diagnosed by a professional mechanic.
* Other sensors: Other sensors, such as the coolant temperature sensor, can affect the ECU's idle control calculations.
Troubleshooting steps:
1. Check the easy things first: Inspect the air filter, vacuum hoses, and throttle body for obvious problems. Clean or replace as needed.
2. Clean the throttle body: This is a crucial step and often resolves idle issues. Use throttle body cleaner and follow the instructions carefully.
3. Check for vacuum leaks: Use a vacuum gauge or spray carb cleaner around vacuum hoses while the engine is running. A rising RPM indicates a leak.
4. Diagnose the IAC valve: Testing an IAC valve requires some specialized tools or knowledge. A mechanic or a detailed online guide specific to your EA82 engine (the engine in your 1986 Subaru GL Wagon) will be necessary.
5. Consider the TPS: If cleaning the throttle body and checking vacuum hoses don't resolve the issue, suspect the TPS. Again, testing this often requires specialized equipment.
In summary: You can't directly adjust the idle speed. Focus on identifying and fixing the underlying problem causing the incorrect idle speed. Because this is an older car with a computer-controlled system, you might benefit from consulting a repair manual specific to your 1986 Subaru GL Wagon or seeking the help of a mechanic familiar with older Subarus. Attempting repairs without the proper knowledge could cause further damage.
