Diagnostic Procedures

Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM.

NOTE: Ensure engine speed stabilizes with each commanded RPM change to determine if engine speed stays within 100 RPM of the commanded RPM.

Set parking brake and block drive wheels. Install scan tool. Start engine. Turn OFF all of the accessories. With the scan tool in RPM control function, slowly increment engine speed to 1700 RPM, then to 600 RPM, then to 1700 RPM. Exit the RPM control function. Does the engine speed stabilize within 100 RPM of the commanded RPM during the above test? If yes, go to next step. If no, go to step 4.
Observe the Freeze Frame/Failure Records for this DTC. Turn ignition off for 30 seconds. Start engine. Operate the vehicle within the Conditions for Running DTC or as close to the Freeze Frame/Failure Records data that you observed. See CONDITIONS FOR RUNNING DTC . Does the DTC fail this ignition cycle? If yes, go to next step. If no, see DIAGNOSTIC AIDS .
Turn ignition off. Disconnect the IAC valve. Connect an IAC Motor Driver (J-37027-1A) to the IAC valve. Start engine. With IAC Motor Driver, command the IAC valve in until about 600 RPM is reached. Using the IAC Motor Driver, command the IAC valve out until about 1700 RPM is reached. Return engine speed to desired idle as indicated on the scan tool data list. Did the engine speed steadily decrease to near 600 RPM and steadily increase to near 1700 RPM when the IAC valve was commanded in and out? If yes, go to next step. If no, go to step 11.
With a test light connected to ground, probe one of the IAC valve circuits at the IAC valve harness connector using the Connector Test Adapter Kit (J-35616-A). Start engine. With the IAC Motor Driver, command low RPM while observing a scan tool until the IAC counts start to increment. With the IAC Motor Driver, command high RPM while observing a scan tool until the IAC counts start to increment. While the IAC counts are incrementing, observe the test light. Return engine idle speed to desired idle as indicated on the scan tool data list. Repeat procedure for the other 3 IAC valve circuits. Did the test light remain ON, never flashing, while the IAC counts where incrementing at any of the IAC valve circuits during the above test? If yes, go to step 10. If no, go to next step.
Did the test light remain OFF, never flashing, while the IAC counts where incrementing at any of the IAC valve circuits during the above test? If yes, go to step 9. If no, go to next step.
Connect a test light between the IAC coil "A" low circuit and IAC coil "A" high circuit. With the IAC Motor Driver, command low RPM while observing a scan tool until the IAC counts start to increment. With the IAC Motor Driver, command high RPM while observing a scan tool until the IAC counts start to increment. While the IAC counts are incrementing, observe the test light. Return engine idle speed to desired idle as indicated on the scan tool data list. Repeat the procedure with the test light connected between the IAC coil "B" low circuit and the IAC coil "B" high circuit at the IAC valve harness connector. Return engine speed to the desired idle as indicated on the scan tool data list. Did the test light stay illuminated and never flashing while the IAC counts where incrementing during the above test? If yes, go to next step. If no, go to step 16.
Inspect for a poor connection at the IAC valve harness connector. Did you find and correct the condition? If yes, go to step 17. If no, go to step 12.
Turn ignition off. Disconnect the PCM harness connectors. With a DVOM, test the circuit where the test light remained OFF for the following:
- An open circuit.
- A short to ground.
- A short to another IAC valve circuit.
After repairs, go to step 17.
Turn ignition on. With a DVOM, test the circuit where the test light remained ON for the following:
- A short to voltage.
- A short to another IAC valve circuit.
Did you find and correct the condition? If yes, go to step 17. If no, go to step 12.
Visually and physically inspect for the following:
- Throttle body damage and tampering.
- Throttle lever screw tampering, if equipped.
- Restricted air intake system. Inspect for a possible collapsed/clogged air intake duct, before and after the air filter element, restricted air filter element, restriction at the throttle body intake screen, if equipped.
Remove the IAC valve. Inspect for the following conditions:
- A clogged IAC passage.
- Excessive deposits on the throttle plate.
- Excessive deposits in the throttle bore.
- Excessive deposits on IAC valve pintle.
Repair any of the conditions as necessary. Did you find and correct the condition? If yes, go to step 17. If no, go to step 14.
Inspect for a poor connection at the PCM harness connectors. Did you find and correct the condition? If yes, go to step 17. If no, go to next step.
Disconnect the PCM harness connectors. With a DVOM, test all IAC valve circuits for high resistance. Did you find and correct the condition? If yes, go to step 17. If no, go to step 16.
Inspect for a poor connection at the IAC valve harness connector. Did you find and correct the condition? If yes, go to step 17. If no, go to next step.
Replace the IAC valve. See REMOVAL & INSTALLATION - MONTANA, SILHOUETTE & VENTURE article. After repairs, go to step 17.
Replace PCM. See REMOVAL & INSTALLATION - MONTANA, SILHOUETTE & VENTURE article. Reprogram PCM. See POWERTRAIN CONTROL MODULE under PROGRAMMING. After repairs, go to next step.
Clear the DTCs with a scan tool. Turn ignition off for 30 seconds. Start engine. Operate the vehicle within the Conditions for Running DTC. See CONDITIONS FOR RUNNING DTC . Does the DTC run and pass? If yes, go to next step. If no, go to step 2.
Observe the stored information, Capture Info with a scan tool. Does the scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.