Mechanics

Idle Air Control Motor IAC Replacement

How to Replace an Idle Speed Control Motor IAC

The idle air control motor or idle speed control motor is designed to adjust the air flow into the intake manifold. This in turn adjusts the speed (RPM) of the engine at idle. The PCM or powertrain control module monitors the engine speed and commands the idle air control motor to move one way or the other to open or close the valve to achieve the desired rpm. The idle speed control motor is usually mounted on the intake manifold near the throttle body. The air bypass port in the throttle body is used to feed the idle speed control motor. An idle air control motor can malfunction causing the engine either to idle too high or too low and stall out

An idle air control motor is usually simple to replace or service. A condition called "coking" is a normal occurrence of a thin build up of a tar like substance which  is a normal by-product of processing large amounts of air. When this condition is present it must be cleaned with a cleaner such as carburetor cleaner and by using a shop towel. After removing the idle air control motor open the butterfly plate and clean both sides of the plate and the bore itself along with the idle air control inlet and outlet passages.

(Note: if your car is a "drive by wire" meaning no throttle cable is used, your car is not equipped with a idle air control motor valve).
(Note: On some Ford vehicles when the idle air control motor fails to will make a "moaning" or "honking" sound)

Before we begin, start with the car on level ground in park with the emergency brake set. The engine should be warm or cold but not hot. You will be dealing with cleaning solvents so please wear protective clothing, gloves and eyewear.


Tools and Supplies to Complete this Job

1. Wrench Set

2. Socket and Ratchet Set

3. Screwdriver Set

4. Cleaning Solvent such as Carburetor Cleaner

5. Replacement Idle Air Control Motor Valve

6. Shop Towels
 

Instructions

Step 1 - Locate and release the hood release latch cable. Then release the secondary hood release and raise the hood, support with prop rod if necessary.

Step 2 - Then, identify the location of the idle air control motor. If you cannot find it you might need to use a component locator in a car repair manual. Most of the time is it near the throttle body or air intake tube.

Step 3 - Once the idle air control motor is located remove the electrical connector from the idle air control motor valve.

Step 4 - Using a wrench or socket remove the two or three mounting bolts.

Step 5 - Next, lightly tap or pry on the valve to "pop" it loose and remove the valve.

Step 6 - Thoroughly clean the gasket surface and the inlet and outlet ports. Be carful to not allow gasket debris to enter the ports.

Step 7 - Remove the new idle speed control valve from its packaging and compare the old valve with the new one. If the electrical connector and the mounting holes are the same you should be in good shape. Sometimes manufacturers can update the design of the valve, so it might look slightly different.

Step 8 - Install the new gasket onto the intake plenum. (This gasket might need to be held in place with gasket sealer).

Step 9 - Next, install the new idle air control valve using the mounting bolts and tighten as needed.

Step 10 - Reinstall the electrical connector.

Once the job is complete the idle air control valve will need to recalibrate itself. You can do this by starting the engine. The engine might idle too high, or stall out. This is ok because the computer has not learned the new valve settings yet. If the engine stalls, try holding your foot on the throttle to help the engine run long enough for the computer to take over. If the engine idle is too high give the engine a chance to warm up and the computer will start to lower the idle. Additionally, it can take some time for the engine idle to return to normal operating characteristics. After a few short drives the engine idle will return to normal.

Best Practices

  • Always clean the throttle body and idle air ports inside the intake manifold plenum.
If further assistance is needed, our certified car repair technicians are ready to answer your car questions. Also, gain manufacturer specific instructions and information by clicking - Auto Repair Manual

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AUTHOR


Written by
Co-Founder and CEO of 2CarPros.com
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


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Article first published (Updated 2013-08-16)