Chrysler Full-Size Trucks 1989-1996 Repair Guide

Idle Air Control (IAC) Motor

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OPERATION



See Figures 1 and 2

The IAC motor is mounted to the throttle body and is operated by the engine controller. The throttle body has an air control passage that provides air for the engine at idle (when the throttle plate is closed). The IAC motor pintle protrudes into the air control passage and regulates air flow through it. Based on various sensor inputs, the engine controller adjusts engine idle speed by moving the IAC motor pintle in and out of the air control passage. The IAC motor is positioned when the ignition key is turned to the ON position.



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Fig. Fig. 1: The IAC motor-3.9L, 5.2L and 5.9L engines



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Fig. Fig. 2: Location of the IAC motor-8.0L engine

Never attempt to adjust the engine idle speed using the factory adjusted set screw.

A factory adjusted set screw is used to mechanically limit the position of the throttle body throttle plate. All idle speed functions are controlled by the engine controller.

TESTING



See Figures 3 and 4

The IAC motor is mounted to the throttle body.

To perform a complete test of the IAC motor, you will need the DRBII scan tool, or equivalent. This test is a test of the IAC motor only. You will need access to the special factory IAC motor exerciser tool No. 7558.



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Fig. Fig. 3: A typical hookup of the IAC motor exerciser tool No. 7558

Take the following precautions before beginning:



Set the parking brake and block the drive wheels.
 
Route all tester cables away from the cooling fan(s), drive belt(s), pulleys and exhaust system.
 
Do not operate the engine indoors, but provide proper ventilation.
 
Always return the engine idle speed to normal before disconnecting the exerciser tool.
 

  1. With the ignition OFF , unplug the IAC motor wire connector at the throttle body.
  2.  
  3. Plug the exerciser tool No. 7558 harness connector onto the IAC motor (see refer to the accompanying illustration)
  4.  
  5. Connect the red clip of the exerciser tool to the positive battery terminal and the black clip to the negative terminal. The red lamp will be illuminated when it is properly connected.
  6.  
  7. Start the engine. When the switch is in the high or low position, the lamp on the exerciser tool will flash. This indicates that the voltage pulses are being sent to the IAC stepper motor.
  8.  



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Fig. Fig. 4: IAC stepper motor pintle

  1. Move the switch to the HIGH position. The engine speed should increase. Move the switch to the LOW position. The engine speed should decrease.
    1. If the engine speed changed predictably while using the exerciser tool, the IAC motor is working correctly. Disconnect the exerciser tool and connect the IAC stepper motor wire to the stepper motor.
    2.  
    3. If the engine speed does not change, turn the ignition OFF and proceed to the step No. 6. Do not disconnect the exerciser from the IAC stepper motor.
    4.  

  2.  

WARNING

With the IAC motor removed from the throttle body, do not extend the pintle more than 0.250 in. (6.35mm). If the pintle is extended more than this amount, it may separate from the IAC stepper motor and the motor will have to be replaced.

  1. Remove the IAC stepper motor from the throttle body.
  2.  
  3. With the ignition OFF , cycle the exerciser tool switch between the HIGH and LOW positions. Keep your attention on the pintle. It should move in-and-out of the motor.
    1. If the pintle does not move, replace the IAC motor. Start the engine and test the replacement motor operation as described in step No. 5.
    2.  
    3. If the pintle operates properly, check the IAC motor bore in the throttle body bore for blockage and clean as needed. Install the IAC motor and retest. If blockage is not found, more complete testing will be required using the DRBII scan tool, or equivalent and the appropriate Powertrain Diagnostics Procedures service manual.
    4.  

  4.  

REMOVAL & INSTALLATION



The IAC motor is mounted to the throttle body.

  1. Remove the air cleaner housing and tube assembly.
  2.  
  3. Unplug the electrical connector from the IAC motor.
  4.  
  5. Remove the mounting bolts.
  6.  
  7. Remove the IAC motor from the throttle body.
  8.  

To install:
  1. Install the IAC motor to the throttle body. Install and tighten the bolts to 60 inch lbs. (7 Nm).
  2.  
  3. Engage the electrical connector and then the air cleaner assembly.
  4.  

 
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