Chart C2C - Idle Air Control
The ECM will control engine idle speed by moving the Idle Air Control (IAC) valve to control air flow around the throttle plate. It does this by sending voltage pulses to the proper motor winding for each IAC motor. This will cause the motor shaft and valve to move IN or OUT of the motor a given distance for each pulse received.
The ECM uses the following information to control idle speed; Battery voltage, Coolant temperature, Manifold Absolute Pressure (MAP), Throttle Position Sensor, Engine speed, A/C clutch signal. Do not apply battery voltage across the ICA motor terminals. This will permanently damage the motor windings.
NOTE:
The following step numbers refer to the numbers in the accompanying flow chart(s).
- Be sure to disconnect the IAC valve prior to this test. The test light will confirm the ECM signals by a steady or flashing light on all circuits.
- Before replacing an ECM, be sure to check the resistance at the IAC motor windings. Failure to do so may result in a repeat ECM failure.
- Diagnostic Aids. Engine idle speed can be adversely affected by the following: Faulty P/N switch, Leaking injectors, Vacuums leaks, Binding or sticking throttle shaft or throttle position sensor, Faulty EGR valve, Faulty battery cables, Loss of A/C compressor signal during load.