GM Malibu/Cutlass 1997-2000

Idle Air Control (IAC) Valve

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OPERATION



The engine idle speed is controlled by the PCM through the Idle Air Control (IAC) valve mounted on the throttle body. The PCM sends voltage pulses to the IAC stepper motor causing the IAC motor shaft and pintle to move in or out a given distance (number of steps) for each pulse, (called counts). The pintle is extended to reduce idle and retracts the pintle to raise the idle.

This movement controls air flow around the throttle plate, which in turn, controls engine idle speed, either cold or hot. IAC valve pintle position counts can be seen using a scan tool. Zero counts corresponds to a fully closed passage, while 140 or more counts (depending on the application) corresponds to full flow.

TESTING





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Fig. Test the Idle Air Control (IAC) valve resistance between A and B and terminals C and D. The resistance should be 20-80 ohms



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Fig. Test the Idle Air Control (IAC) valve resistance between B and C and terminals A and D. The resistance should be infinite

  1. Disengage the IAC valve electrical connector.
  2.  
  3. Using an ohmmeter, measure the resistance between IAC valve terminals A and B . Next measure the resistance between terminals C and D .
  4.  
  5. Verify that the resistance between both sets of IAC valve terminals is 40-60 ohms. If the resistance is not as specified, the IAC valve may be faulty.
  6.  
  7. Measure the resistance between IAC valve terminals B and C . Next measure the resistance between terminals A and D .
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  9. Verify that the resistance between both sets of IAC valve terminals is infinite. If the resistance is not infinite, the IAC valve may be faulty.
  10.  
  11. Also, with a small mirror, inspect IAC valve air inlet passage and pintle for debris. Clean as necessary, as this can cause IAC malfunction.
  12.  

REMOVAL & INSTALLATION





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Fig. The IAC is located on the throttle body-3.1L engine shown, 2.4L similar



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Fig. When installing a new IAC valve, measure the distance between the tip of the valve pintle and the mounting flange. The distance should be 1.10 inch (28mm)



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Fig. Use finger pressure to slowly retract the pintle until the measurement is within specification


WARNING
If the IAC valve has already been in service, do not push or pull on the valve pintle. The force required to move the pintle may damage the threads on the worm drive. Also do not soak the IAC in solvent or any liquid solvent or damage may result.

  1. Disconnect the negative battery cable.
  2.  
  3. Detach the IAC valve electrical connector.
  4.  
  5. Unfasten the two screws attaching the IAC valve to the throttle body.
  6.  
  7. Remove the IAC valve and O-ring.
  8.  

To install:

  1. Lubricate the new IAC valve O-ring with clean engine oil and install to the IAC valve.
  2.  
  3. Install the IAC valve to the throttle body.
  4.  
  5. Install the IAC attaching screws and tighten to 27 inch lbs. (3 Nm).
  6.  
  7. Re-attach the electrical connector.
  8.  
  9. Connect the negative battery cable.
  10.  
  11. Reset the IAC valve pintle position, as follows:
    1. Turn the ignition switch to the ON position (engine OFF ).
    2.  
    3. Turn the ignition switch to the OFF position for 10 seconds.
    4.  
    5. Start the vehicle and check for proper idle operation.
    6.  

  12.  

 
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