GM Grand Am/Achieva/Calais/Skylark/Somerset 1985-98

Idle Air Control (IAC) Valve

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OPERATION



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.

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 transmission in neutral or automatic transmission 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.

TESTING



See Figures 1 and 2

Click image to see an enlarged view

Fig. Fig. 1: First test the IAC terminals A and B



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Fig. Fig. 2: Next test terminals C and D of the IAC

  1. Attach an ohmmeter to the top two prongs of the IAC valve, terminals A and B.
  2.  
  3. Inspect the ohms, measurements should be between 50-80 ohms.
  4.  
  5. Repeat the process for the two lower terminals, C and D.
  6.  
  7. If the sensor does not come within specifications on either of these tests, replace the component.
  8.  

REMOVAL & INSTALLATION



Throttle Body Injection

See Figure 3

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the air cleaner assembly.
  4.  
  5. Detach the electrical connection from the idle air control assembly.
  6.  
  7. Unfasten the retaining screws, then remove the idle air control valve from the throttle body assembly. Discard the O-ring.
  8.  
  9. Clean the IAC valve O-ring sealing surface, pintle valve seat and air passage.
  10.  

Be sure that the cleaner is safe to use on systems equipped with an oxygen sensor. Do not use a cleaner containing methylethylketone.

  1. Use a suitable carburetor cleaner and a parts cleaning brush to remove the carbon deposits. Shiny spots on the pintle or on the seat are normal and do not indicate a misalignment or a bent pintle shaft. If the air passage has heavy deposits, remove the throttle body for a complete cleaning.
  2.  



Click image to see an enlarged view

Fig. Fig. 3: View of a flange mount IAC valve

To install:

Before installing a new idle air control valve, measure the distance that the valve is extended. This measurement should be made from motor housing to end of the cone. The distance should be no greater than 11/8 in. (28mm). If the cone is extended too far, damage to the valve may result. The IAC valve pintle may also be retracted by using IAC/ISC Motor Tester J-37027/BT-8256K. It is recommended not to push or pull on the IAC pintle. However, the force required to retract the pintle of a NEW valve should not cause damage. Do not soak the IAC valve in any liquid cleaner or solvent, as damage may result.

  1. Be sure to identify the idle air control valve and replace with an identical part. The IAC valve pintle shape and diameter are designed for specific applications.
  2.  
  3. Lubricate a new IAC valve O-ring with clean engine oil.
  4.  
  5. Install the new idle air control valve, apply Loctite 262 or equivalent to the retaining screws, then tighten them to 27 inch lbs. (3 Nm).
  6.  
  7. Attach the electrical connection.
  8.  
  9. Install the air cleaner assembly.
  10.  
  11. Connect the negative battery cable.
  12.  
  13. The base idle will not be correct until the ECM resets the IAC. To reset the IAC valve pintle position proceed as follows:
    1. Block the drive wheels, then apply the parking brake firmly.
    2.  
    3. Start the engine, then hold the engine speed above 2,000 rpm. Ground the diagnostic test terminal (ALDL) for ten seconds, then remove the ground.
    4.  
    5. Turn the ignition OFF , then restart the engine and check for proper idle operation.
    6.  

  14.  

Multi-Port Injection

See Figures 4 through 9

  1. Disconnect the negative battery cable.
  2.  



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Fig. Fig. 4: View of the Idle Air Control (IAC) valve mounting in the throttle body assembly



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Fig. Fig. 5: IAC valve air flow diagram

  1. Detach electrical connector from idle air control valve.
  2.  
  3. Unfasten the retaining screws, then remove the idle air control valve from its mounting position.
  4.  



Click image to see an enlarged view

Fig. Fig. 6: There are two types of IAC valves; one has a collar at the electric terminal end and one doesn't

To install:

WARNING
If re-installing the used IAC valve, 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 valve in any liquid cleaner; this will damage the valve

  1. If installing a new idle air control valve, measure the distance the valve plunger is extended. Measurement should be made from the edge of the valves mounting flange to the end of the cone. The distance should not exceed 1 1 /8 in. (28mm), or damage to the valve may occur when installed. If measuring distance is greater than specified above, use finger pressure to slowly retract the pintle, by using a slight side to side motion to help it retract easier (valve with collar at electric terminal end) or compress the retaining spring from the valve while turning the valve "in" with a clockwise motion. Return the spring to its original position with the straight part of the spring end aligned with the flat surface of the valve (valve without collar at electric terminal end).
  2.  



Click image to see an enlarged view

Fig. Fig. 7: Adjusting a new IAC valve-with collar



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Fig. Fig. 8: For new IAC valves without a collar, compress the retaining spring from the valve while turning the valve "in" with a clockwise motion, then ...



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Fig. Fig. 9: ... return the spring to its original position with the straight part of the spring end aligned with the flat surface of the valve

  1. Use a new gasket, then position the idle air control valve in its mounting position.
  2.  
  3. Install the retaining screws, then tighten them to 27 inch lbs. (3 Nm).
  4.  
  5. Attach the IAC valve electrical connector.
  6.  
  7. Connect the negative battery cable.
  8.  
  9. For most vehicles, the idle may be unstable for up to 7 minutes upon restarting, while the ECM resets the IAC valve pintle to the correct position.
  10.  
  11. For vehicles equipped with a 3.0L engine, reset the IAC valve by turning the ignition switch ON , and then OFF .
  12.  
  13. For 1990-95 2.3L vehicles you must reset the IAC valve pintle position as follows:
    1. Turn the ignition switch to the ON position (engine off).
    2.  
    3. Ground the diagnostic test terminal (ALDL) for five seconds, then remove the ground.
    4.  
    5. Turn the ignition OFF for ten seconds.
    6.  
    7. Start the engine and check for proper idle operation.
    8.  

  14.  

Sequential Injection

See Figures 10 and 11

If installing a new IAC valve, be sure to replace with an identical part. IAC valve pintle shape and diameter are designed for the specific application.

  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.  
  7. Use a suitable carburetor cleaner and parts cleaning brush to clean carbon deposits from the valve. Shiny spots on the pintle seat are normal and do not indicate a need for replacement.
  8.  



Click image to see an enlarged view

Fig. Fig. 10: If installing a new valve, measure the distance between the tip of the IAC valve pintle and mounting flange



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Fig. Fig. 11: The IAC valve and TP sensor are mounted to the throttle body

  1. Inspect the IAC valve O-ring for damage, and replace if necessary.
  2.  

To install:

CAUTION
If re-installing the old IAC valve, 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 valve in any type of liquid cleaner or solvent, as this may damage the valve.

  1. If installing a new valve, measure the distance between the tip of the IAC valve pintle and mounting flange. If the distance is greater than 1 1 /8 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 IAC valve O-ring with clean engine oil, then position on the valve.
  4.  
  5. Install the IAC valve assembly and secure with the retaining screws. Tighten the screws to 27 inch lbs. (3 Nm).
  6.  
  7. Attach the valve electrical connector.
  8.  
  9. Connect the negative battery cable, then reset the IAC valve pintle position as follows:
    1. Turn the ignition ON for five seconds.
    2.  
    3. Turn the ignition OFF for ten seconds.
    4.  
    5. Start the engine and check for proper idle operation.
    6.  

  10.  

 
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