Subaru Coupes/Sedans/Wagons 1985-1996 Repair Guide

Idle Air Control (IAC) Valve

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OPERATION



See Figure 1

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Fig. Fig. 1: Idle air control valve (1) above the throttle position sensor (2)-Legacy

The IAC valve increases engine speed when engine temperature is low by venting air into the air duct behind the throttle plate.

On the Loyale, the IAC valve is located on top of the engine, in front of intake air duct. On the Justy, it is in-line between the air filter housing and the intake manifold. On the Impreza, Legacy and SVX, the IAC valve is incorporated into the throttle body.

TESTING



Electrical Type
  1. Disconnect the electrical harness to the IAC valve while the engine is idling. Check to see that the rpm drops.
  2.  
  3. Connect the IAC valve connector and check to see that engine rpm resumes its original speed.
  4.  

Disconnecting the harness causes a change in engine rpm when the engine is cold. However, when the engine is warm, it causes a smaller change, or almost no change at all.

  1. Stop the engine, then disconnect the electrical harness from the IAC valve.
  2.  
  3. Turn the ignition switch to the ON position.
  4.  
  5. Using a voltmeter, measure the voltage across power terminal BW on the IAC valve connector and ground. Voltmeter should read 10 volts. If the voltage obtained is less than specified, check the harness.
  6.  
  7. Turn the ignition switch to the OFF position. Using an ohmmeter, measure the resistance between each terminal of the connector on the IAC valve. The ohmmeter should read 7.3-13 ohms at -4°F-176°F (-20°C-80°C). If specifications are not as specified, replace the IAC valve.
  8.  
  9. Using an ohmmeter, measure the insulation resistance between each terminal of the connector on the IAC valve and ground. The ohmmeter should read 1 mega-ohm. If specifications are not as specified, replace the IAC valve.
  10.  
  11. Connect the IAC valve harness, then disconnect the control unit electrical harness.
  12.  
  13. Turn the ignition switch to the ON position. Using a voltmeter, measure the voltage between terminal 45 (GR) of the control unit harness and ground. Voltmeter should read 10 volts. If specifications are not as specified, check the harness between the IAC valve and the control unit.
  14.  
  15. Turn the ignition switch to the OFF position, then connect the control unit harness.
  16.  
  17. Monitor the voltage across terminal 45 (GR) on the control unit harness and ground, when the ignition switch is turned to the ON position. Voltmeter should read 1 volt for approximately 1 minute after the ignition switch is turned ON and 10 volts after 1 minute. If specifications are not as specified, check for poor contact of the terminal or a faulty control unit.
  18.  
  19. Turn the ignition switch to the OFF position, then disconnect the IAC valve hose.
  20.  
  21. Turn the ignition switch to the ON position. Look through the open end of the pipe (from which the air control pipe was disconnected) and check that the valve moves from the fully closed position to the fully opened position, 1 minute after the ignition switch is turned to the ON position.
  22.  

REMOVAL & INSTALLATION



  1. Disconnect the negative battery cable.
  2.  
  3. Disconnect the injector lead wire from the clamp.
  4.  
  5. Remove the IAC valve, gasket and lead wire from the venturi chamber.
  6.  

To install:
  1. Using a new gasket, install the IAC valve.
  2.  
  3. Connect the injector lead wire.
  4.  
  5. Connect the negative battery cable.
  6.  

 
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