GM IAC Reset Procedure: When Needed and How to Do?

The idle air control valve (IAC) is an important part of the car's engine. It is attached to the engine throttle and will regulate the airflow of the vehicle when it is not in motion. This helps to control the speed of the engine when the car is stationary and creates smooth idling. Sometimes, the IAC can develop problems that require it to be reset. How do you know the IAC needs to be reset?

Engine electrical problems highlights

• Level of urgency:high
• DIY inspection:possible but complicated
• DIY repairs:impossible
• Can you drive?yes, if it starts
• Price of repairs:$150 - $650
• If ignored:no-start, harsh work, warning lights
• Ways to fix:good scanning for codes, professional repairs

What is the Idle Air Control Valve?

The idle air control valve is an engine component that is located on the throttle body. It works with the car's ECM to control the airflow into the engine when the vehicle is idling. Depending on the oxygen needs of the engine, the idle air control valve will open or close to adjust the amount of air that flows into the engine.

A properly functioning idle air control valve will regulate the speed of the engine, preventing it from burning too much fuel while idling and it will also ensure a smooth idle.

How Do I Know if My Idle Air Control Valve Needs to be Reset?

A functioning idle air control valve is necessary for smooth idling to occur. If the IAC valve is not working properly, you will notice many different problems in the engine, especially when idling or accelerating from a stop.

Here are some of the problems you might notice if your idle air control valve needs to be reset:

• Your engine accelerates slowly from a stop.
• Your engine stalls frequently.
• Your engine idles erratically or roughly.
• Your engine's idle speed is erratic or higher than normal.
• Your car's fuel economy has decreased.
• The check engine light is on.

A problem with the idle air control valve will make the engine's behavior less predictable, especially when idling or starting to move from an idle. This makes it more difficult to drive the car. In order to continue driving your car safely, you will need to reset the IAC valve.

The idle air control valve might also need to be reset if you have recently removed or replaced it. This will calibrate the new IAC valve to the Engine Control Unit.

How to Test if the IAC Needs to Be Reset

If you notice the symptoms of a malfunctioning idle air control valve in your car, you'll need to confirm whether the IAC valve actually needs to be reset. This is because other problems can result in these symptoms as well.

Before you try to reset your car's IAC valve, there is a simple test you can perform to check whether the valve is working properly.

• Turn on the car and allow the engine to idle.
• Turn off the radio and the air conditioning so that you can hear the engine.
• Listen to the sound of the engine and note whether it sounds regular or irregular.
• Pay attention to the engine's RPM. The RPM should be between 600 and 1200.

If the sound of the engine is irregular, and the RPMs are not in the normal range, then there is probably an issue with the IAC valve. In this case, you can go ahead to reset the valve.

How to Reset GM Idle Air Control Valve

Most cars produced after the year 2000 will reset the idle air control valve themselves. If you drive a GM car, such as a Cadillac, Chevrolet, or GMC, produced before the year 2000, then you'll need to follow this procedure to reset the IAC.

Resetting the IAC for an older GM vehicle requires connecting two pins on the car's ALDL connector. While this is safe to do, and relatively simple, it is easier to faster to attempt resetting the IAC without grounding the pins first.

How to Reset GM Idle Air Control Valve Without Grounding the ALDL

Here are two methods that you can use to reset the IAC if you don't have a diagnostic tool.

• Press the accelerator pedal down slightly for four seconds.
• Release the accelerator pedal.
• Start the engine and let it run for five to 10 seconds.
• Turn off the ignition.
• Wait for 10 seconds.
• Restart the engine.

If this method does not work, there is another method you can try if you do not have an ALDL.

• Start with the engine.
• Turn off the engine.
• Turn on the ignition, but do not start the engine.
• Press the accelerator pedal four or five times.
• Release the accelerator pedal.
• Start the engine.

While these are good general methods for resetting the idle air control valve in most types of vehicles, these methods might not work for a GM vehicle. If these methods fail to reset the idle air control valve in your GM car, you will need to reset the IAC valve by grounding the ALDL.

How to Reset GM Idle Air Control Valve by Grounding the ALDL

GM vehicles from before 1995 make use of an ALDL connector for scanning trouble codes. Resetting the IAC requires you to short two pins in the ALDL connector.

The exact procedure is different pending on the make and model of the vehicle. To determine the exact process for your vehicle, you will need to look up the IAC reset procedure for your makeup model.

Here is the general procedure that works for most GM vehicles.

• Ground the ALDL diagnostic lead. You can do this by using a length of wire to bridge the two pin connectors in the top right corner of the ALDL connector. This is safe to do and won't cause any damage to the car.
• Turn on the ignition, but don't start the engine.
• Wait 30 seconds.
• With the ignition still on, disconnect the IAC electrical connector.
• Remove the grounding from the ALDL terminal.
• Start the car.
• Turn off the car, then disconnect the battery and reconnect the IAC connector.
• Reconnect the battery and start the car.

How to Clean Idle Air Control Valve?

The IAC valve might malfunction because it has become jammed or gummed up with debris and carbon deposits. In order to get it working again, it will need some maintenance and cleaning.

When the engine is idling, carbon deposits can build up on the IAC valve. This could cause the valve to get stuck in either the open or closed position. To restore the proper function of the valve, you will need to clean off the carbon deposits and other debris that is causing the valve to get stuck.

To locate and properly clean the valves, you should consult the owner's manual.

Here are some general steps you can follow to clean the IAC valve in most GM vehicles.

• Locate the idle air control valve. The owner's manual should give you the precise location of the valve in your own vehicle. However, it is located near the air intake of most cars.
• Disconnect the electrical connector of the IAC valve. You may need a screwdriver to do this.
• Using a screwdriver or wrench, disconnect the screws and bolts that hold the IAC valve in position.
• Consult the owner's manual to find out whether you can use a carburetor cleaner or a throttle body cleaner on your car's idle air control valve. If these cleaners are suitable for your IAC, then spray your cleaner into the valve.
• Using a brush, gently remove the carbon deposits from the valve. Continue to spray and use the brush until the valve is clean.
• Once the cleaning solution has dried off the valve, you can reinstall it into the car. Make sure to reattach every bolt and screw you removed and reconnect the valve's electrical connector.

Conclusion

The idle air control valve bypasses the throttle and controls the airflow to the engine when it is idling. It regulates the engine speed when idling, which produces a smooth idle and prevents the engine from consuming too much fuel.

If the IAC valve is showing symptoms of malfunctioning, resetting it will usually get it to start functioning properly. Some symptoms of a bad IAC valve are rough idling, high RPMs, stalling, and weak acceleration. You might also need to reset the idle air control valve if you have recently removed or replaced the IAC.

There are three different methods of resetting the IAC valve. The first two methods are very simple and work for most cars. The last method works only for older GM vehicles and requires you to ground two pins in the ALDL connector.