How to Service an Automotive Engine Idle Air Control Valve

The idle air control valve is responsible for controlling the engine idle speed via the car's PCM (computer). These valves are configured differently depending on manufacturer but perform the same task. The IAC or ISC valve as it's called diverts engine intake air from the main throttle body and bypasses a portion of the intake air to control idle speed. When the idle speed cannot be controlled it will trigger a check engine light (MIL) due to idle speed fluctuations. On newer cars (2000 - 2005) depending on manufacturer this valve is being phased out as electronic throttle systems are becoming commonplace.

What goes wrong?

As a car ages the IAC will become dirty (a condition called coking) due to the volumes of air processed through the valve. Heavy particles in the air attach themselves to the valve's internal parts making it difficult for the valve to operate.

Where is it?

The idle air control valve (IAC) is located near the throttle body of the intake manifold in most cases. Additional designs include rubber hoses running from the throttle body and air intake tube to a remote valve.

What's the cost?

The cost of an IAC will vary but typically will run between $60.00 and $120.00 US. If you are not changing the valve yourself labor costs will be minimal because of the easy access to the valve. If the valve is mounted to the bottom of the throttle bore such as in Toyota products the cost will run slightly more. To service the IAC separately the cost should be applicable to the vales location. Most services of this kind are included in a major tune up.

Getting Started

Locate the IAC valve on your engine. If your car does NOT have a throttle cable you do not have an IAC valve, this is the best way to tell what kind of system your car has. For this example we have removed the throttle bore and cleaned it, once completed remove the mounting screws to the idle air control valve. You might need to use a impact screwdriver to get the screws undone.
This image shows the coking condition similar to the throttle actuator/bore which causes erratic operation of the valve, stalling and high idle can be the result.
Use carburetor cleaner to spray the valves internal parts using a shop towel to help wipe away deposits (clean the valve thoroughly). This can take some time so you may need to let the valve soak in cleaner depending on the level of coking while other idle air valves need to be replaced due to internal wear.
The IAC gathers air from internal ports inside the intake and throttle bore systems. These transfer ports need to be serviced as well when cleaning the IAC motor to help keep the newly cleaned valve working correctly.
Make sure all gaskets or seals are in good shape to avoid leakage as you reinstall the valve onto the throttle bore housing and reinsert the mounting screws to tighten evenly.