Sienna 1998-1999

Idle Air Control Valve

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Operation



Specific to:

Toyota Sienna 1998-2005

The IAC valve assembly controls the engine idle speed. The IAC valve assembly meters intake air around the throttle plate through a bypass within the IAC valve assembly and throttle body. The ECM determines the desired idle speed or bypass air and signals the IAC valve assembly through a specified duty cycle. The IAC valve responds by positioning to control the amount of bypassed air. The ECM monitors engine RPM and increases or decreases the IAC duty cycle in order to achieve the desired RPM.

Removal & Installation



Specific to:

Toyota Sienna 1998-2005

  1. Before servicing the vehicle, refer to the precautions.
  2.  
  3. Remove the throttle body.
  4.  
  5. Remove the 4 screws, bracket, IAC valve and gasket.

    Click image to see an enlarged view

    Fig. IAC location

  6.  

To install:

  1. Installation is the reverse of removal.
  2.  
  3. Install a new gasket on the throttle body.
  4.  

Testing



Specific to:

Toyota Sienna 1998-2005

  1. Check that the IAC valve is half opened.
  2.  
  3. Connect the IAC valve connector to the IAC valve.
  4.  
  5. Turn the ignition switch ON.
  6.  
  7. Check that the IAC valve moves in 0.5 seconds by order of fully close, fully open and half open.
  8.  
  9. If operation is not as specified, replace the IAC valve.
  10.  
  11. Turn the ignition switch OFF.
  12.  
  13. Disconnect the IAC valve connector from the IAC valve.

    Click image to see an enlarged view

    Fig. IAC testing

  14.  

 
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