How to Test if the Idle Speed Motor is Faulty?
3 Answers
After turning on the ignition switch, the starter motor spins at high speed but the engine crankshaft does not respond. This phenomenon indicates a malfunction in the starter motor's transmission mechanism; The starter motor operates abnormally, and the drive gear does not rotate; Insufficient power output from the starter motor prevents it from driving the crankshaft. A short circuit in the field winding or battery power loss may lead to inadequate starter motor power.
Last time my car's idle speed kept fluctuating, and I suspected the idle air control valve was faulty, so I decided to test it myself. After starting the engine, I gently pressed and released the throttle to observe the tachometer's movement—if the idle speed was unstable or fluctuated violently between 500-1000 RPM, there was a high chance the valve had issues. Next, I leaned under the hood to listen for any continuous humming or hissing sounds near the valve's location; if there was no sound at all, it was likely dead. Before removing the valve, I first checked for loose wiring or carbon buildup, using compressed air to clean it and see if symptoms improved. Remember, during testing, ensure the car is parked stably and in neutral, and don't let the engine overheat. If cleaning doesn’t help, it’s best to buy a used replacement for a trial fit—this can save a lot on repair costs, since new valves aren’t expensive anyway. The key is to ensure stable idling and avoid stalling on the road.
With years of experience in car repair, the most common method I use to diagnose idle control valve failure is connecting an OBD scanner. After starting the engine, check for trouble codes like P0505 or other idle control valve-related errors - the results appear immediately. Another simple test is turning the key to the ON position without ignition, waiting for the dashboard self-check lights to go off, then manually pushing the valve lever of the motor - there should be slight resistance or minimal movement feel under normal conditions. If it's stuck or loose, it's defective. For a more professional approach, use a multimeter to measure the motor's resistance: unplug the connector and measure between the two pins - the resistance should read 10-15 ohms. Infinite resistance or abnormally low readings indicate internal short circuit or open circuit. Don't attempt disassembly yourself as it may damage other electronic components. The safest option is to have it replaced at a repair shop, especially for older vehicles where aged wiring poses higher risks - improper handling could cause system-wide errors which would be troublesome.
