* Idle air control valve (IACV): The IACV is responsible for controlling the amount of air that bypasses the throttle body at idle. If the IACV is dirty or faulty, it can cause the engine to idle erratically.
* Vacuum leak: A vacuum leak can cause the engine to run lean, which can lead to high idle speeds. Check for vacuum leaks around the intake manifold, throttle body, and vacuum hoses.
* Faulty oxygen sensor: The oxygen sensor measures the amount of oxygen in the exhaust gas. If the oxygen sensor is faulty, it can send incorrect signals to the engine computer, which can cause the engine to run rich or lean.
* Fuel injector problems: A faulty fuel injector can cause the engine to run lean or rich, which can lead to high idle speeds. Check the fuel injectors for leaks or clogs.
If you're not sure what is causing your Honda CRX 1988 rpm to go up and down, it's best to take it to a qualified mechanic for diagnosis.
