Jeep Wagoneer/Commando/Cherokee 1984-1998

Idle Air Control (IAC) Valve



The Idle Air Control valve, or IAC valve is mounted on the back of the throttle body. The valve controls the idle speed of the engine by controlling the amount of air flowing through the air control passage. There is a factory pre-set throttle screw located by the valve which is not connected with the valve and should never be tampered with.

The IAC valve consists of electronic motors that move a pintle shaped plunger in and out of the air control passage. The valve receives an electronic signal from the PCM.

When the valve plunger is moved in, the air control passage flows more air. This raises the idle speed. When the valve plunger is moved out, the air control passage flows less air. This lowers the idle speed.


  1. Verify that there are no vacuum leaks or other mechanical problems that can affect the idle speed.
  3. Start the engine, let it warm to a normal operating temperature and observe the idle speed.
  5. Turn on various consumers such as the A/C system, high beams and/or the rear window defroster and observe the idle speed.
  7. With the brake pedal firmly depressed, place the vehicle in gear (automatic transmission) or place the vehicle in fourth gear and slightly disengage the clutch (manual transmission). Observe the idle speed. Return the transmission to park or neutral.
  9. If the idle speed does not immediately return to specification, the IAC valve may be faulty.

Removal & Installation

See Figure 1

  1. Remove the air intake duct at the throttle body.
  3. Disengage the IAC valve wiring connector, remove the two mounting screws and carefully pull the valve from the throttle body.
  5. Installation is the reverse of removal.

Click image to see an enlarged view

Fig. Fig. 1: Removing the IAC valve from the throttle body