How to Check an IAC Valve

by Rachel Moon

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 buildup, 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.


Disconnect the negative battery cable.


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.


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.


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


Examine the pointed seating end of the IAC for buildup. Use carburetor cleaner to remove any deposits that could prevent a clean seal.


Disconnect the negative battery cable.


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

Items you will need

About the Author

Since 1996 Rachel Moon has worked as a technical writer and technical editor in such diverse fields as the semiconductor industry, chemical delivery equipment and video game community management. She has developed curriculum for Occupational Safety and Health Administration general industry training after getting certification from the University of California, San Diego, Southwest Safety Training Alliance and an automotive/diesel vocational school. Moon attended Hofstra University.

Photo Credits

  • photo_camera New car petrol engines image by Christopher Dodge from