Instead of trying to adjust the idle, you should diagnose the underlying cause. Here's what to check:
* Clean the throttle body: A dirty throttle body can cause erratic idle. Clean it with throttle body cleaner, following the instructions carefully. Disconnect the battery negative terminal before starting.
* Check the air intake system: Make sure there are no leaks in the air intake system between the air filter and the throttle body. A leak can cause a lean condition affecting the idle.
* Inspect the PCV valve: A faulty PCV (Positive Crankcase Ventilation) valve can introduce excess air into the intake, affecting the idle. Replace it if necessary.
* Check the mass airflow sensor (MAF) sensor: A dirty or faulty MAF sensor provides inaccurate air flow readings to the ECM, leading to poor idle. Clean it carefully (with MAF sensor cleaner) or replace it if necessary.
* Inspect vacuum lines: Check all vacuum lines for cracks or leaks. A leak can disrupt the engine's vacuum system and affect idle.
* Check the IAC (Idle Air Control) valve: While you can't adjust it directly, a faulty IAC valve is a common cause of idle problems. It's usually best to replace it if suspect.
* Scan for trouble codes: Use an OBD-II scanner to read any diagnostic trouble codes (DTCs) stored in the ECM. These codes will pinpoint potential problems. Auto parts stores often offer free code scanning.
* Battery voltage: Low battery voltage can sometimes cause erratic idle. Have your battery and charging system tested.
Important Note: If you're not comfortable working on your vehicle, take it to a qualified mechanic. Improperly attempting to adjust or fix the idle system can cause further damage. The ECM controls many aspects of engine operation, and interfering without proper knowledge can be detrimental.
