GM Cavalier/Sunbird/Skyhawk/Firenza 1982-1994

Idle Air Control (IAC) Valve

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OPERATION



See Figure 1

Engine idle speeds are controlled by the computer control module (ECM/PCM) through the IAC valve mounted on the throttle body. The ECM or PCM sends voltage pulses to the IAC motor windings causing the IAC motor shaft and pintle to move in or out a given distance (number of steps) for each pulse (called counts). The movement of the pintle controls the airflow around the throttle plate, which in turn, controls engine idle speed. Idle air control valve pintle position counts can be observed using a scan tool. Zero (0) counts corresponds to a fully closed passage, while 140 counts or more correspond to full flow.



Click image to see an enlarged view

Fig. Fig. 1: Schematic of the IAC valve air flow

Idle speed can be categorized in 2 ways: actual (controlled) idle speed and minimum idle speed. Controlled idle speed is obtained by the ECM positioning the IAC valve pintle. Resulting idle speed is determined by total air flow (IAC passage + PCV + throttle valve + calibrated vacuum leaks). Controlled idle speed is specified at normal operating conditions, which consists of engine coolant at normal operating temperature, air conditioning compressor OFF, manual transaxle in neutral or automatic transaxle in D.

Minimum idle air speed is set at the factory with a stop screw. This setting allows enough air flow by the throttle valves to cause the IAC valve pintle to be positioned a calibrated number of steps (counts) from the seat during normal controlled idle operation.

The idle speed is controlled by the computer control module through the IAC valve. No adjustment is required during routine maintenance. Tampering with the minimum idle speed adjustment is highly discouraged and may result in premature failure of the IAC valve.

REMOVAL & INSTALLATION



See Figure 2

  1. Disconnect the negative battery cable.
  2.  
  3. Detach the IAC valve electrical connector.
  4.  
  5. Unfasten the IAC valve retaining screws, then remove the valve.
  6.  


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

Click image to see an enlarged view

Fig. Fig. 2: Idle Air Control (IAC) valve components


  1. Clean the IAC valve O-ring sealing surface, pintle valve seat and air passage. You can clean the valve using GM cleaner 1052626, GM X-66A or equivalent. Use clean shop towel or parts cleaning brush to remove any heavy deposits. If the air passage has heavy deposits, remove the throttle body for complete cleaning.
  2.  
  3. Inspect the O-ring for damage and replace, if necessary.
  4.  

To install:

If you're installing a new IAC valve, you must replace it with an identical part. IAC valve pintle shape and diameter are designed for the specific application.

  1. If you are installing a new IAC valve, measure the distance between the tip of the valve and the mounting flange. If it is greater than 1.10 in. (28mm), use finger pressure to slowly retract the pintle. The force required to retract the pintle of a NEW valve will not cause damage to the valve.
  2.  
  3. Lubricate the O-ring with clean engine oil, then position on the valve.
  4.  
  5. Install the IAC valve assembly, then secure using the attaching screws. Tighten the screws to 27 inch lbs. (30 Nm).
  6.  
  7. Attach the valve 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 OFF for ten seconds.
    4.  
    5. Start the engine and check for proper idle operation.
    6.  

  12.  

 
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