GM S-Series Pick-ups and SUV's 1994-1999 Repair Guide

Idle Air Control (IAC) Valve

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OPERATION



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



See Figures 1, 2 and 3

  1. Disengage the IAC electrical connector.
  2.  
  3. Using an ohmmeter, measure the resistance between IAC terminals A and B . Next measure the resistance between terminals C and D .
  4.  
  5. Verify that the resistance between both sets of IAC terminals is 20-80 ohms. If the resistance is not as specified, the IAC may be faulty.
  6.  
  7. Measure the resistance between IAC terminals B and C . Next measure the resistance between terminals A and D .
  8.  
  9. Verify that the resistance between both sets of IAC terminals is infinite. If the resistance is not infinite, the IAC may be faulty.
  10.  
  11. Also, with a small mirror, inspect IAC air inlet passage and pintle for debris. Clean as necessary, as this can cause IAC malfunction.
  12.  



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Fig. Fig. 1: 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. Fig. 2: Test the Idle Air Control (IAC) valve resistance between B and C and terminals A and D. The resistance should be infinite



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Fig. Fig. 3: Idle Air Control (IAC) valve wiring and terminal identification

REMOVAL & INSTALLATION



See Figures 4 through 11



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Fig. Fig. 4: Unfasten the IAC valve screws and ...



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Fig. Fig. 5: ... remove the IAC valve



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Fig. Fig. 6: The IAC valve can be on the throttle body, usually next to the throttle position sensor-1996-97 4.3L engine shown



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Fig. Fig. 7: Location of the IAC valve-1996-97 2.2L engine shown



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Fig. Fig. 8: Location of the IAC valve-1998-99 2.2L engine shown

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the air cleaner assembly or resonator as necessary.
  4.  
  5. Unplug the electrical connection.
  6.  
  7. Remove the IAC valve. On thread-mounted units, use 1 1 / 4 in. (32mm) wrench and on flange-mounted units, remove the screw assemblies.
  8.  
  9. Remove the IAC valve gasket or O-ring and discard it.
  10.  

To install:
  1. Clean the old gasket material from the surface of the throttle body assembly on the thread mounted valve. On the flange-mounted valve clean the surface to ensure proper O-ring sealing
  2.  
  3. If installing a new IAC valve, measure the distance between the tip of the valve pintle and the mounting flange. If the distance is greater than 1.10 inch (28mm), use finger pressure to slowly retract the pintle until the measurement is within specification (refer to the accompanying illustration).
  4.  
  5. Install the valve with a new gasket or O-ring. Tighten the thread mounted assembly 13 ft. lbs. (18 Nm) and tighten the flange mounted attaching screws to 28 inch. lbs. (3 Nm).
  6.  
  7. Engage the electrical connector to the IAC valve.
  8.  
  9. Connect the negative battery cable.
  10.  



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Fig. Fig. 9: 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. Fig. 10: Use finger pressure to slowly retract the pintle until the measurement is within specification

  1. If removed, install the air cleaner or resonator.
  2.  
  3. On 1998-99 models to set the pintle position, turn the ignition key to the ON engine OFF for five seconds. Turn the ignition key to the OFF position for ten seconds, then start the engine and check for proper idle operation.
  4.  



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Fig. Fig. 11: If installing a new IAC valve, measure the distance between the valve pintle and mounting flange. If adjustment is required, use finger pressure to retract the pintle until the measurement is within specification

 
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