![]() ![]() The driver circuit can be tested with a noid light or a digital oscilloscope to see if the PCM is sending a digital control signal to the ISC motor or solenoid. This doesn’t happen very often, but the driver circuit may be damaged if one of the wires that carries voltage in the ISC control circuit shorts or grounds out. Unfortunately, some technicians just replace the ISC motor or solenoid before checking these other possibilities, and then discover it didn’t fix the fault.Īnother possible cause of ISC-related stalling problems would be a bad ISC driver circuit in the PCM. If the wiring harness appears to be good, and the ISC solenoid or motor is receiving a signal from the PCM - but is not responding - you can assume the fault is a bad ISC motor or solenoid.Replacing a perfectly good ISC motor or solenoid won’t fix the problem if the fault is in the wiring. Look up the ISC circuit wiring diagram for the vehicle, and check for voltage and ground at the appropriate terminals. Problems here can prevent the PCM command signal from reaching the ISC solenoid or motor. Check the idle speed control system wiring harness and connector to make sure it’s tight and corrosion-free.But if the ISC system still fails to respond to your command to increase idle speed, or fails to maintain normal idle speed, there’s a problem that will require further diagnosis before you replace any parts. ![]() If the engine now idles normally, and you can command idle speed changes, you’ve fixed the problem (a dirty idle bypass port or valve). Then start the engine and repeat the idle speed test. ![]() Let the cleaner soak for at least 10 minutes before giving it another blast of cleaner. Use the small plastic tube that attaches to the nozzle on the aerosol can to aim the cleaner directly into the bypass port(s). Aim for the little air bypass holes in the throttle opening.
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