The IAC stepper motor is mounted to the throttle body, and regulates the amount of air bypassing the control of the throttle plate. As engine loads and ambient temperatures change, engine RPM changes. A pintle on the IAC stepper motor protrudes into a passage in the throttle body, controlling air flow through the passage. The IAC is controlled by the Powertrain Control Module (PCM) to maintain the target engine idle speed.
Removal & Installation
- Remove air resonator box at throttle body.
- Disconnect the electrical connector from the Idle Air Control (IAC) motor.
- Remove the mounting screws and remove the IAC from the throttle body.
- Installation is the reverse of removal procedure.
- Tighten the two mounting bolts (screws) to 60 inch lbs. (7 Nm).
- Start the engine and allow it to idle for at least 60 seconds. Using a diagnostic scan tool, check for the presence of any Diagnostic Trouble Codes (DTCs). Record and address these codes as necessary.
- Turn the ignition off and remove the Air Cleaner Assembly from the Throttle Body. Check for any broken components in the Throttle Body. Check for any signs of a foreign material (ice, dirt, or excessive carbon build up) on the Throttle Plate or in the bore causing the Throttle Plate to stick.
- Remove and inspect the air cleaner. Replace if necessary.
- Remove the Idle Air Control (IAC) motor and check the resistance across the motor pin terminals. If the resistance is not between 8.7 and 10.7 ohms, replace the IAC motor.
- Refer to any Technical Service Bulletins (TSBs) that may apply.
- Review the scan tool Freeze Frame information. If possible, try to duplicate the conditions under which the DTC set.
- With the engine running at normal operating temperature, monitor the scan tool parameters related to the DTC while wiggling the wire harness. Look for parameter values to change and/or a DTC to set. Turn the ignition off.
Visually inspect the related wire harness. Disconnect all the related harness connectors. Look for any chafed, pierced, pinched, partially broken wires and broken, bent, pushed out, or corroded terminals.
Perform a voltage drop test on the related circuits between the suspected inoperative component and the PCM.
CAUTIONDo not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install Miller Special Tool No. 8815 to perform diagnosis.
- Inspect and clean all PCM, engine, and chassis grounds that are related to the most current DTC.
- If numerous trouble codes were set, use a wire schematic and look for any common ground or supply circuits.
- For any Relay DTCs, actuate the Relay with the scan tool and wiggle the related wire harness to try to interrupt the actuation.
- For intermittent Evaporative Emission trouble codes perform a visual and physical inspection of the related parts including hoses and the Fuel Filler cap.
- Use the scan tool to perform a System Test if one applies to failing component. A co-pilot, data recorder, and/or lab scope should be used to help diagnose intermittent conditions.