Volvo 240/740/760/780/940/960 1990-1998

Idle Air Control Valve

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OPERATION



See Figure 1



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Fig. Fig. 1: A typical IAC valve assembly

An Idle Air Control (IAC) valve is incorporated into the system to set the correct air valve opening and constant idle speed. The valve consists of a stepper motor with twin coils, one for opening and one for closing. The ECM delivers pulsed ground signals to both IAC coils. Depending on the signals from the ECM, the motor operates a rotary valve which controls the air flow through the outlet port.

In the event of an electrical fault, a spring maintains the rotary valve in a fixed position and the idling speed is increased to approximately 1200 RPM. The ECM incorporates a self-learning system which enables it to learn the ideal idling speed. Because of this feature, the IAC valve is not adjustable.

TESTING



See Figures 2, 3, 4, 5 and 6

  1. Disconnect the negative battery cable.
  2.  
  3. Unplug the IAC connector.
  4.  
  5. To test the coil driver circuits in the IAC valve:
    1. Using an ohmmeter, measure the resistance between pins 3 and 2 on the IAC valve.
    2.  
    3. Resistance should be 10-14 ohms. If resistance is ok, proceed to the next step. If resistance is out of range, replace the IAC and retest.
    4.  
    5. Using an ohmmeter, measure the resistance between pins 1 and 2 on the IAC valve.
    6.  
    7. Resistance should be 10-14 ohms. If resistance is ok, proceed to the next step. If resistance is out of range, replace the IAC and retest.
    8.  

  6.  
  7. To test the voltage lead:
    1. Using an voltmeter, measure the voltage at terminal 2. Turn the ignition ON , and measure the voltage between terminal 2 and ground.
    2.  
    3. Voltage should be battery voltage. If voltage is not present or out of range, repair the circuit. If voltage is ok, proceed to the next step.
    4.  

  8.  
  9. To test the signal return:
    1. Using an voltmeter, measure the voltage at terminal 1. Turn the ignition ON , and measure the voltage between terminal 1 and ground.
    2.  
    3. Voltage should be around 6.0-8.5v. If voltage is not present or out of range, repair the circuit. If voltage is ok, proceed to the next step.
    4.  

  10.  
  11. To test the ground circuit:
    1. Using an ohmmeter, measure the resistance at terminal 3. Turn the ignition ON , and measure the resistance between terminal 1 and ground.
    2.  
    3. Resistance should be 0 ohms. If continuity is not present or out of range, repair the circuit. If continuity is ok, replace the CMP sensor and retest.

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      Fig. Fig. 2: IAC valve terminal (pin) identification



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      Fig. Fig. 3: IAC valve connector terminal identification



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      Fig. Fig. 4: Testing the coil driver circuit between pins 2 and 3



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      Fig. Fig. 5: Testing the coil driver circuit between pins 2 and 1



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      Fig. Fig. 6: Testing the IAC valve circuit at terminal 2 of the harness connector

    4.  

  12.  

REMOVAL & INSTALLATION



See Figure 7

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the throttle pulley cover (if equipped).
  4.  
  5. Remove the connector from the IAC.
  6.  
  7. Remove the hoses from the IAC valve.
  8.  
  9. Remove the IAC valve from the mounting hardware.
  10.  

To install:
  1. Place the IAC valve in the mounting hardware and secure it.
  2.  
  3. Install the hoses to the IAC.
  4.  
  5. Install the connector on the IAC.
  6.  
  7. Install the throttle pulley cover (if removed).
  8.  
  9. Connect the negative battery cable.
  10.  



Click image to see an enlarged view

Fig. Fig. 7: Location of the IAC valve-850 models

 
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