Volkswagen Cars 2000-05

Idle Air Control Valve

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Operation



The Idle Air Control (IAC) valve controls the amount of air that bypasses the throttle valve, which controls the engine idle speed. The IAC valve consists of windings, an armature, a return spring, and a rotary slide. The engine control module (ECM) pulses the voltage to the winding, the opposing forces on the armature by the return spring cause it to maintain a fixed position, adjusting the amount of bypass air to maintain the correct idle speed.

Removal & Installation



  1. Turn the ignition switch to the OFF position.
  2.  
  3. Disconnect the idle air control valve harness electrical connector.
  4.  
  5. Using a suitable tool, remove idle air control valve.
  6.  
  7. Installation is in reverse order of removal.
  8.  

Testing



Checking Idle Air Control Valve (IAC) Triggering
  1. Check IAC valve is electrically OK.
  2.  
  3. Slide up boot on the IAC valve connector.
  4.  



Click image to see an enlarged view

Fig. IAC Connector

  1. Use scan tool 'Output Diagnostic Test Mode' function 03 to trigger the IAC valve - N71.
  2.  
  3. Connect VAG 1527B voltage tester, or equivalent, between terminal 1 and engine ground (GND). Voltage tester must flash.
  4.  
  5. Connect VAG 1527B voltage tester, or equivalent, between terminal 2 and battery positive voltage (B+). Voltage tester must light up.
  6.  
  7. If specified results are not obtained:
  8.  
    1. Connect VAG 1598/19 test box, or equivalent, to ECM harness connector.
    2.  
    3. Check the wiring between harness and connector terminal 1 (in engine compartment) to test box socket D11 . Then check the wiring between harness connector terminal 2 and test box socket D9 using wiring diagram. Repair as necessary.
    4.  
    5. If the wiring is okay, but triggering still does not occur, replace the ECM.
    6.  
    7. If the triggering signal and the wiring are okay and the valve does not react, replace the IAC valve.
    8.  


Checking Mechanical Function
  1. Remove the idle air control (IAC) valve.
  2.  
  3. Visually check the surface of the rotary slide (arrow) for signs of wear.
  4.  



Click image to see an enlarged view

Fig. Showing the IAC Valve


WARNING
Do NOT check for ease of movement by prying on the rotary slide with a screwdriver or other tools that could cause scratching or other damage.

  1. Reconnect the IAC valve, while still removed, to the harness connector.
  2.  
  3. Use scan tool 'Output Diagnostic Test Mode' function 03 to trigger IAC valve - N71.
  4.  
  5. Check whether rotary slide moves freely from stop to stop.
  6.  
  7. If there are signs of scoring, or if the rotary slide does not move freely in both directions, replace the IAC valve.
  8.  
  9. If the IAC valve does not respond (not triggered) during the Output Diagnostic Test Mode, check triggering.
  10.  

Resistance Test
  1. Remove the idle air control valve harness connector.
  2.  
  3. Use a suitable Digital Multimeter (DMM) to measure the resistance between the 2 terminals of the idle air control valve.
  4.  
  5. The correct measurement should be 7-11 ohms. If not, replace the idle air control valve.
  6.  


NOTE
At room temperature, the resistance value will be lower. The resistance value will be higher if the Idle Air Control (IAC) valve is measured at under-hood operating temperatures.

  1. Reconnect the idle air control valve harness connector.
  2.  
  3. The idle air control valve should hum and vibrate slightly when the ignition is turned 'ON'. If not, the ECM or harness may be defective.
  4.  

Testing with VAG1551:

  1. Remove the idle air control valve harness connector.
  2.  
  3. Connect the VAG 15278 LED tester to terminals 1 and 2 of the harness connector using the jumpers from VW 1594 adaptor kit.
  4.  
  5. Turn ignition ON, perform steps from output DTM (Diagnostic Test Mode) to activate the IAC valve (N71) LED tester must blink.
  6.  
  7. If tester does not blink, check wiring using VAG 1598 pin out box, electrical checks, step 26. Repair as necessary.
  8.  
  9. If wiring is okay, replace the ECM.
  10.  
  11. If LED tester blinks but the IAC valve does not operate, replace the IAC valve.
  12.  

 
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