Idle Air Control (IAC)


The Idle Air Control (IAC) valve controls the engine idle speed and dashpot functions. The valve is located on the side of the throttle body. This valve allows the necessary amount of air, as determined by the Powertrain Control Module (PCM) and controlled by a duty cycle signal, to bypass the throttle plate in order to maintain the proper idle speed.

Idle Air Control Sensor Symptoms

  • Stalls after start when engine is cold
  • Stalls after start when engine is hot
  • Stalling on deceleration
  • Stalls at idle
  • Unstable idle
  • Diesels or runs on after the engine is shut off
  • High idle
  • Low idle

Idle Air Control Testing

  1. Turn the ignition switch to the OFF position.
  2. Disengage the wiring harness connector from the IAC valve .
  3. Using an ohmmeter, measure the resistance between the terminals of the valve.

    NOTE: Due to the diode in the solenoid, place the ohmmeter positive lead on the VPWRterminal and the negative lead on the ISC terminal.

  4. If the resistance is not 7–13 ohms, replace the IAC valve.

    The following symptoms can be caused by a faulty IAC due to loose connections, bad grounds, high resistance in the circuit, or opens in the circuit.

    Idle Air Control Sensor Replacement

    1. Disconnect the negative battery cable.
    2. Disengage the wiring harness connector from the IAC valve.
    3. Remove the two retaining screws, then remove the IAC valve and discard the old gasket.
    4. To install:

    5. Clean the IAC valve mounting surface on the throttle body of old gasket material.
    6. Using a new gasket, position the IAC valve on the throttle body. Install and tighten the retaining screws to 71–106 inch lbs. (8–12 Nm).
    7. Attach the wiring harness connector to the IAC valve.
    8. Connect the negative battery cable.
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