How to check an iac valve

Written by rachel moon
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How to check an iac valve
A quick check of the IAC can help pinpoint engine performance concerns. (New car petrol engines image by Christopher Dodge from

The idle air control, or IAC, valve regulates the amount of air that enters the engine while a vehicle is idling by opening or closing a bypass in the throttle body. Increasing the volume of air entering the engine will increase idle speed, which increases fuel consumption and engine noise. The motor in the IAC valve is susceptible to carbon build-up, which can cause the motor to fail or respond too slowly to engine operating conditions. In turn, this can cause the engine to idle too fast or too slow. In extreme cases, the engine may stall.

Skill level:

Things you need

  • Vehicle service manual
  • Torque wrench
  • Gloves
  • Aerosol carburettor cleaner

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  1. 1

    Disconnect the negative battery cable.

  2. 2

    Locate the IAC's electrical connector. It is usually found on or near the throttle body. Disconnect the electrical connector. Reconnect the negative battery cable.

  3. 3

    Turn the ignition key to "On" but do not start the engine. Observe the IAC. If it moves in and out, the IAC is good. If it does nothing, replace the unit and try again.

  4. 4

    Remove the IAC completely. Spray the carburettor cleaner into the IAC passages while wearing gloves to protect your skin.

  5. 5

    Examine the pointed seating end of the IAC for build-up. Use carburettor cleaner to remove any deposits that could prevent a clean seal.

  6. 6

    Disconnect the negative battery cable.

  7. 7

    Reinstall the IAC. Reconnect the electrical connector. Reconnect the negative battery cable.

Tips and warnings

  • If you have access to an OBD II scan tool, you can use it to pull codes that may help with the diagnosis of the idle air control system.
  • On some vehicles, you should not disconnect the battery cable before performing this procedure. Check the vehicle service manual for more information.
  • Do not allow carburettor cleaner to contact your bare skin or eyes. Avoid inhalation. Follow all precautions on the label.

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