1. Vacuum leak: A vacuum leak can cause the engine to run lean, which can lead to a high idle speed. Check all vacuum hoses and connections for leaks.
2. Idle air control valve (IAC valve): The IAC valve controls the amount of air that bypasses the throttle body at idle. If the IAC valve is stuck open, it can cause the engine to idle too high. Test the IAC valve to see if it is working properly.
3. Throttle body: The throttle body controls the amount of air that flows into the engine. If the throttle body is dirty or obstructed, it can cause the engine to idle too high. Clean the throttle body and check for any obstructions.
4. Oxygen sensor: The oxygen sensor monitors the amount of oxygen in the exhaust gas. If the oxygen sensor is faulty, it can cause the engine to run rich, which can lead to a high idle speed. Test the oxygen sensor to see if it is working properly.
5. Engine coolant temperature sensor: The engine coolant temperature sensor (ECT sensor) monitors the temperature of the engine coolant. If the ECT sensor is faulty, it can cause the engine to run rich or lean, which can lead to a high idle speed. Test the ECT sensor to see if it is working properly.
