Idle Air Control Valve

What is an idle air control valve and where is it located?

The idle air control valve (IAC) allows air to flow to the engine while the car is idling or decelerating, such as when you encounter a stop light or leave the car running (in park, of course) while you rush in the house to grab that lunch you forgot. During acceleration, the throttle body controls the flow of air to the engine. When the throttle is not activated, the throttle plate is closed and does not allow air to pass to the engine. The engine, of course, requires air to combust fuel. So, there must be some bypass that lets air in while the engine is idling, and that’s where the idle air control valve comes in.

Your vehicle’s engine control unit (ECU), the onboard computer, will receive information from various sensors and then control the action of the idle air control valve to allow air to the engine. This keeps the engine idling at the proper rate of revolutions per minute. To accomplish this, the IAC valve contains a small electric motor that moves a valve to open and close it. If the IAC valve isn’t working, the engine might idle roughly or stall.

In fuel-injected vehicles, the IAC valve is most often found attached to the throttle body itself, or close to it. In older carbureted cars, it is found on the throttle linkage and In this case it is most commonly referred to as an idle speed control (ISC) valve, or simply as an idle speed controller, though this terminology is also used on fuel-injected engines as well.

In addition, there are many other automotive slang words used with these devices, depending on the make, model and engine involved. The most common are:

• Idle air control (IAC) motor, idle air control (IAC) actuator, and idle air control (IAC) solenoid
• Idle speed control (ISC) motor, idle speed control (ISC) actuator, and idle speed control (ISC)
  solenoid. Chrysler uses “automatic” in front of these terms, so you may hear automatic idle speed
  (AIS) motor, valve, actuator or solenoid when it comes to Chrysler models.
• You may also see the word “sensor” used with these devices, though it could actually be a different
  part depending on the vehicle / other words that go with it. In actuality, these devices don’t “sense”
  anything.

How do I know if my idle air control valve needs to be replaced?

There are a number of signs that something has gone wrong with your idle air control valve. As you may have already surmised, these problems will come to your attention when you are idling. The car may idle roughly, meaning that the car vibrates or shakes at idle. If the problem gets worse, you might find that the engine’s RPMs dip and the engine stalls when you’re stopped, causing everyone to honk their horns at you when the traffic light turns green. As a simple test, you can try lightly pressing the accelerator when the RPMs start to drop. If it returns to a normal level, and then starts to dip too low again, that can be a sign of an IAC valve problem. The correct idle speed will vary from one engine to another but is usually between 600 and 1,000 RPMs. You can check the IAC valve at home with a voltmeter, if you happen to have one on hand.

The most common cause for idle speed control valve problems is simply the valve itself becoming clogged with dirt, rust, or oil build up. This prevents the valve from opening and closing properly. The motor and electrical wiring inside the ISC valve that controls the valve may also wear out and fail. 

Can I replace an adle air control valve myself?

Yes, replacing the idle air control motor should prove fairly easy. For safety’s sake, disconnect the battery and let the engine cool before working in the engine bay. Replacing the IAC motor will then be a simple matter of disconnecting the wiring harness, unbolting the part, and attaching the new one. When this is done, you might want to check that the engine idles properly.