Idle Air Control System Check

Circuit Description
The Powertrain Control Module (PCM)/Engine Control Module (ECM) controls engine idle speed with the Idle Air Control (IAC) valve. To increase the idle speed, the PCM/ECM pulls the IAC pintle away from its seat, allowing more air to pass by the throttle bore. To decrease the idle speed, it extends the IAC valve pintle toward its seat, reducing bypass air flow. A scan tool will read the PCM/ECM commands to the IAC valve in counts. The higher counts indicate more air bypass (higher idle). The lower counts indicate less air is allowed to bypass (lower idle).

Diagnostic Aids
If the idle is too high, stop the engine. Fully extend the IAC valve with an IAC tester. Start the engine. If the idle speed is above 800 rpm, locate and repair the vacuum leak. Also, check for a binding throttle plate or throttle linkage or an incorrect base idle setting.

Test Description
The number(s) below refer to step(s) on the diagnostic table.
2. The IAC valve is extended and retracted by the IAC driver. IAC valve movement is verified by an engine speed change. If no change in engine speed occurs, the valve can be removed from the throttle body and tested. Connect the IAC driver to the removed IAC valve and turn the ignition ON. Do not start the engine.
5. This step checks the quality of the IAC valve movement in Step 2. Fully extending the IAC valve may cause an engine stall. This may be normal.
6. Steps 2 and 5 verify proper IAC valve operation. This step checks the IAC circuit for a wiring or PCM/ ECM fault.

Idle Air Control Valve Reset Procedure
Whenever the battery cable or the PCM/ECM connector or the PCM/ECM fuse EF31 is disconnected or replaced, the following idle learn procedure must be performed:
1. Turn the ignition ON for 5 seconds.
2. Turn the ignition OFF for 5 seconds.
3. Turn the ignition ON for 5 seconds.
4. Start the engine in park/neutral (P/N).
5. Allow the engine to run until the engine coolant is above 185 °F (85 °C).
6. Turn the A/C ON for 10 seconds, if equipped.
7. Turn the A/C OFF for 10 seconds, if equipped.
8. If the vehicle is equipped with an automatic transaxle, apply the parking brake. While pressing the brake pedal, place the transaxle in drive (D).
9. Turn the A/C ON for 10 seconds, if equipped.
10. Turn the A/C OFF for 10 seconds, if equipped.
11. Turn the ignition OFF The idle learn procedure is complete.

Steps 1 - 10:

Steps 11 - 19:

IDLE AIR CONTROL SYSTEM CHECK