1. Vacuum leaks: Vacuum leaks can cause the idle to fluctuate because they allow unmetered air to enter the engine. This can lean out the air/fuel mixture and cause the engine to run erratically. Check all of the vacuum lines and connections for leaks.
2. Dirty throttle body: A dirty throttle body can also cause the idle to fluctuate. The throttle body is responsible for controlling the amount of air that flows into the engine. When it is dirty, it can restrict the airflow and cause the engine to run lean. Clean the throttle body with a throttle body cleaner.
3. Faulty idle air control valve: The idle air control valve (IACV) is responsible for controlling the amount of air that bypasses the throttle body at idle. When it is faulty, it can cause the idle to fluctuate. Test the IACV according to the manufacturer's specifications.
4. Faulty oxygen sensor: The oxygen sensor is responsible for monitoring the amount of oxygen in the exhaust gas. When it is faulty, it can cause the engine to run rich or lean, which can lead to idle fluctuations. Test the oxygen sensor according to the manufacturer's specifications.
5. Faulty fuel injector: A faulty fuel injector can also cause the idle to fluctuate. When an injector is faulty, it can deliver too much or too little fuel, which can cause the engine to run rich or lean. Test the fuel injectors according to the manufacturer's specifications.
