Toyota Celica 1994-1998 Repair Guide

Idle Air Control (IAC) Valve

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OPERATION



The ECM is programmed with specific engine speed values to respond to different engine conditions (coolant temperature, air conditioner on/off, etc.). Sensors transmit signals to the ECM which controls the flow of air through the bypass of the throttle valve and adjusts the idle speed to the specified value. Some vehicles use an Idle Speed Control (ISC) valve while others use an Air Valve or Idle Air Control (IAC) valve to control throttle body by-pass air flow.

TESTING



7A-FE Engine

See Figures 1, 2, 3, 4, 5 and 6

  1. Using a jumper wire, connect terminals TE1 and E1 of the DLC1.
  2.  



Click image to see an enlarged view

Fig. Fig. 1: View of the common IAC valve

  1. After the engine rpm is kept at 900-1300 for about 5 seconds, check that the rpm returns to idle.
  2.  
  3. If the rpm operation is not as specified, check the IAC valve, wiring and engine ECM.
  4.  
  5. Remove the jumper wire form the DLC1.

    Click image to see an enlarged view

    Fig. Fig. 2: Raise the idle speed between 900 and 1300 rpm for 5 seconds

  6.  

  1. Disconnect the IAC valve wiring.
  2.  



Click image to see an enlarged view

Fig. Fig. 3: Remove the harness from the IAC valve to test the terminals

  1. Using an ohmmeter, measure the resistance between terminals +B and the other terminals (RSC and RSO).
  2.  



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Fig. Fig. 4: Use an ohmmeter to check the IAC valve resistance between terminals-7A-FE engine

  1. Resistance should be between:

    1994-95 models-19.3-22.3 ohms
     
    1996-17.0-24.5 ohms
     

  2.  

  1. If the resistance is not within specifications, replace the IAC valve.
  2.  
  3. To check the operation of the IAC valve, the engine should be at normal operating temperature and the transmission in Neutral.
    1. Connect the positive lead of the battery to terminal B+ and the negative lead to terminal RSC, then check that the valve is closed.
    2.  
    3. Connect the positive lead from the battery to terminal B+ and the negative lead to terminal RSO, then check that the valve is open.

      Click image to see an enlarged view

      Fig. Fig. 5: Testing the IAC valve using battery voltage to see if the valve is closed-7A-FE engine



      Click image to see an enlarged view

      Fig. Fig. 6: Testing the IAC valve using battery voltage to see if the valve is open-7A-FE engine

    4.  

  4.  
  5. If operation is not as specified, replace the IAC valve.
  6.  

5S-FE Engine

See Figures 7, 8 and 9



Click image to see an enlarged view

Fig. Fig. 7: IAC wiring schematic-5S-FE engine

  1. Using a jumper wire, connect terminals TE1 and E1 of the DLC1.
    1. After the engine rpm is kept at 900-1300 for about 5 seconds, check that the rpm returns to idle.
    2.  
    3. If the rpm operation is not as specified, check the IAC valve, wiring and engine ECM.
    4.  
    5. Remove the jumper wire from the DLC1.

      Click image to see an enlarged view

      Fig. Fig. 8: Place a jumper wire on the terminals of the DLC1-5S-FE engine



      Click image to see an enlarged view

      Fig. Fig. 9: IAC valve terminal identification-5S-FE engine

    6.  

  2.  
  3. Disconnect the IAC valve wiring.
    1. Using an ohmmeter, measure the resistance between terminals +B and the other terminals ISCC and ISCO.
    2.  
    3. Resistance should be between:

      1994-95 models-19.3-22.3 ohms
       
      1996-98 models-17.0-24.5 ohms
       

    4.  
    5. If the resistance is not within specifications, replace the IAC valve.
    6.  

  4.  
  5. To check the operation of the IAC valve, the engine should be at normal operating temperature and the transmission in Neutral.
    1. Connect the positive lead of the battery to terminal B+ and the negative lead to terminal ISCC, then check that the valve is closed.
    2.  
    3. Connect the positive lead from the battery to terminal B+ and the negative lead to terminal ISCO, then check that the valve is open.
    4.  

  6.  
  7. If operation is not as specified, replace the IAC valve.
  8.  

REMOVAL & INSTALLATION



See Figures 10, 11 and 12

  1. Disconnect the negative battery cable. Wait at least 90 seconds to work on the vehicle once the cable is disconnected to hinder air bag deployment.
  2.  
  3. Drain the engine coolant.
  4.  
  5. Remove the air cleaner cap and disconnect the control cables.
  6.  
  7. Remove the throttle body, refer to Fuel System .
  8.  
  9. Remove the 4 retaining screws, IAC valve and gasket.
  10.  



Click image to see an enlarged view

Fig. Fig. 10: Remove the 4 screws retaining the IAC valve to the throttle body



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Fig. Fig. 11: Separate the IAC and remove the gasket

To install:
  1. Position a new gasket on the throttle body. Attach the IAC valve and secure.
  2.  



Click image to see an enlarged view

Fig. Fig. 12: Always place a new gasket on the IAC before installation

  1. Attach the throttle body to the engine, refer to Fuel System .
  2.  
  3. Attach the control cables, install the air cleaner cap.
  4.  
  5. Fill the cooling system.
  6.  
  7. Start the engine, top off the cooling system and check operation.
  8.  

 
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