Mitsubishi Pick-ups and Montero 1983-1995 Repair Guide

Idle Air Control Motor (Stepper Motor)

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This motor is found on 3.0L and 3.5L engines

OPERATION

See Figures 1 and 2

The amount of air taken in during idling is regulated by the opening and closing of the servo valve located in the air passage that bypasses the throttle valve. The servo valve is opened or closed by the activation of the stepper motor (incorporated within the idle air control motor) in the forward or reverse (clockwise or counter-clockwise) direction. Battery positive (+) voltage is supplied, by way of the MFI relay, to the coil of the stepper motor. The ECM switches the power transistors on (located within the ECM) in sequential order, and, when current floes to the stepper motor coil, the stepper motor is activated in the forward or reverse direction.

If the number of stepper motor steps increases to 100-200 steps or decreases to 0 steps, the cause is probably a malfunction of the stepper motor or damaged or disconnected wiring of the harness.

If the number of stepper motor steps is outside the standard value, even though the results of checking the harness of the idle air control motor and of the component itself indicates no abnormal condition, the cause is probably one of the following: incorrect adjustment of the standard idling speed, deposits adhering to the throttle valve, air drawn into the intake manifold from a leaking gasket, incomplete combustion inside a cylinder (malfunction of spark plugs, ignition coil, injectors, compression pressure, etc.).



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Fig. Fig. 1: The location of the idle air control motor (stepper motor)-3.0L and 3.5L engines



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Fig. Fig. 2: Internal components of the idle air control motor-3.0L and 3.5L engines

HARNESS TESTING



See Figure 3

  1. Unplug the IAC motor harness connector and the MFI relay connector. By touching the probes of the ohmmeter to both ends of the wiring harness, check for continuity between the IAC motor terminal 2 and 5 to the MFI relay terminal 5 (3.0L 12 valve engines) or MFI relay terminal 3 (3.0L 24 valve and 3.5L engines). If no continuity exists, repair the harness between the three terminals.
  2.  
  3. Unplug the ECM connector, and check for an open or short-circuit to ground between the ECM terminal and the IAC motor terminals:
  4.  

3.0L (12 valve) engines:


ECM terminal 58 and IAC motor terminal 1.
 
ECM terminal 59 and IAC motor terminal 3.
 
ECM terminal 67 and IAC motor terminal 4.
 
ECM terminal 68 and IAC motor terminal 6.
 

3.0L (24 valve) and 3.5L Engines:


ECM terminal 4 and IAC motor terminal 1.
 
ECM terminal 17 and IAC motor terminal 3.
 
ECM terminal 5 and IAC motor terminal 4.
 
ECM terminal 18 and IAC motor terminal 6.
 

  1. If there is a short or open-circuit, repair the above harnesses, otherwise the harness is good.
  2.  
  3. Plug all connectors back into their respective components.
  4.  



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Fig. Fig. 3: The harness side connector and terminal numbering-3.0L and 3.5L engines

COMPONENT TESTING



Actuator Testing
  1. Check that the operating sound of the stepper motor can be heard over the idle air control motor when the ignition switch is turned to the ON position (without starting the engine).
  2.  
  3. If no operating sound can be heard, check the stepper motor drive circuit. (If the circuit is good, a defective stepper motor or ECM is suspected.)
  4.  

Coil Resistance Testing
  1. Unplug the idle air control motor connector and fasten the test harness (Mitsubishi tool MD998463).
  2.  
  3. Measure the resistance between terminal 2 (white clip on test harness) of the connector at the idle air control motor side and terminal 1 (red clip) or terminal 3 (blue clip). The resistance should be 28-33 ohms at 68°F (20°C).
  4.  
  5. Measure the resistance between terminal 5 (green clip) of the connector at the idle air control motor side and terminal 6 (yellow clip) or terminal 4 (black clip). The resistance should be the same as above.
  6.  
  7. If the coil failed either of these tests, replace the idle air control motor.
  8.  

Idle Air Control Motor

See Figures 4, 5 and 6

  1. Remove the throttle body. Refer to Fuel System for instructions.
  2.  
  3. Remove the stepper motor.
  4.  
  5. Fasten the test harness to the idle air control motor harness connector.
  6.  
  7. Connect the positive (+) terminal of a power source (approximately 6 V) to the white or the green clip.
  8.  
  9. While holding the idle air control motor as shown in the illustration, connect a negative (-) power source terminal to each clip in the following sequence, and check whether there is vibration of the stepper motor as a result of activation of the stepper motor.
    1. Connect the negative (-) power source terminal to the red and black clips.
    2.  
    3. Connect the negative (-) power source terminal to the blue and black clips.
    4.  
    5. Connect the negative (-) power source terminal to the blue and yellow clips.
    6.  
    7. Connect the negative (-) power source terminal to the red and yellow clips.
    8.  
    9. Connect the negative (-) power source terminal to the red and black clips.
    10.  
    11. Repeat the test in the reverse (e through a) sequence.
    12.  

  10.  
  11. If vibration is felt as a result of this test, the stepper motor can be considered to be normal.
  12.  



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Fig. Fig. 4: The location of the idle air control motor-3.0L and 3.5L engines



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Fig. Fig. 5: Test the idle air control motor for vibration when the harness is connected to it-3.0L and 3.5L engines



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Fig. Fig. 6: Use Mitsubishi tool MD998463 to test the idle air control motor-3.0L and 3.5L engines

REMOVAL & INSTALLATION



To remove the idle air control motor, the throttle body must first be removed from the intake manifold plenum. Once the throttle body has been removed, the stepper motor unbolts from the it. Label any hoses or cables removed and save the bolts and nuts for re-installation. Attach the new stepper motor to the throttle body. Tighten to 8-10 ft. lbs. (12-14 Nm). Install any parts removed for access to the throttle body.

 
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