Idle Air Control (IAC) Motor

A malfunction in the IAC circuit will set a diagnostic trouble code. For testing procedures, see the TESTS W/CODES article. To check IAC for proper operation, perform the following:

1. Install Tech 1 scan tool. Turn ignition on, with engine off. Check for stored Diagnostic Trouble Code(s) (DTCs). If any code(s) is present, diagnose trouble code first. If code(s) is not present, go to next step.
2. Start engine and let idle. Turn off all accessories. Using scan tool, enter MISC TEST and select IAC SYSTEM. Command engine speed up to 1500 RPM and then to 500 RPM and back to 1500 RPM, while monitoring ENGINE SPEED display on scan tool. If engine speed remains within 50 RPM for each RPM command, fault is not present. If engine speed is not as specified, go to next step.
3. Turn engine off. Disconnect IAC valve. Install Noid Light (J-37027). Start engine. Using scan tool, command engine speed up to 1500 RPM, then to 500 RPM and back to 1500 RPM, while monitoring noid light. If noid light cycles from Red to Green, go to step 5). If noid light does not cycle from Red to Green, go to next step.
4. Check Light Green/Black, Light Blue/White and Light Green/White wires between IAC valve and PCM for open or shorted circuit. Repair as necessary. If circuit is okay, check terminal contact at PCM connector C1. Repair as necessary. If terminal contacts are okay, replace PCM and verify proper IAC valve operation.
5. Inspect throttle body for tampering, restriction in air intake system and throttle body for blockage or excessive deposits in IAC passage or throttle bore. Repair as necessary. If passages are okay, check for poor terminal contact at IAC harness connector. Repair as necessary. If connections are okay, replace IAC valve.