Idle Air Control Valve Symptoms And Repair Methods

Idle Air Control Valve Symptoms And Repair Methods

Did you know that you don’t need to replace an IAC valve to repair it completely? Rather, you can clean it with a degreaser, and its performance will get significantly better. If you don’t get it fixed on time, an IAC valve malfunction will cause you a great hassle.

Thus, in this article, we will also not just teach you how to repair an IAC valve but will also take you through a step-by-step guide teaching you how to replace it properly. We will go through an Idle air control valve’s symptoms and repair techniques when it malfunctions and everything that comes in between.

What is an idle air control valve?

Before we get into the details of the idle air control valve symptoms and repair, it’s imperative we understand what an IAC is and why it’s important. An IAC or idle air control valve is responsible for managing the engine’s rotational speed. Previously when cars had carburetors installed, an idle speed screw was used to control the idle speed. Usually, an IAC valve’s placement is near or on the intake manifold’s throttle body.

Now, let us finally discuss all the possible Idle Air Control Valve Symptoms and Repair methods when it becomes faulty. 

Idle Air Control Valve Symptoms and Repair methods

We will first shed some light on the symptoms of a faulty IAC and then move on to discuss all the possible repair and replacement methods.

Symptoms of a faulty IAC Valve

Irregular Idle Speed

One of the most common and evident symptoms of a faulty IAC valve is that you’ll notice an irregularity in the idle speed. Since the IAC valve is responsible for managing the engine’s idle speed, an IAC valve’s dysfunction will disrupt the speed. The IAC valve will no longer have adequate control over the idle speed. Consequently, the idle speed will either be too high or too low.

Engine starts stalling

Engine freezing or stalling is another symptom of a problematic IAC valve. An adequate amount of fuel mixture and air are required for the engine to work properly. In case of the valve fails, the car’s engine will not get the required amount of air to function properly and thus. The engine will start to freeze or stall or may not start at all.

Stalling due to overload

The engine can still function with a malfunctioned IAC valve. However, it will bear more load than usual. If the load increases, the car may stop working at all. A sign of overload is that the steering wheel pushes on one side more.

Increased pressure on the brake pedal

If you are applying more pressure on the brake pedal, that indicates that the car is idling faster than usual. It also consequently means the car’s speed is more than usual.

Rides aren’t smooth

When the IAC valves are properly functional, the car’s engine will perform efficiently, resulting in smoother rides and making your car faster. However, in case of a damaged or faulty valve, the vehicle will stop moving smoothly, and you will also notice vibrations and fluctuations.

Warning Light activation

The check engine warning light will ignite if it detects any IAC valve abnormalities.

Tools needed

To repair or replace an IAC valve, you need the following tools.

  • Socket and a rachet
  • A new IAC valve
  • Throttle cleaner
  • Pliers

Repairing an IAC valve

Replacing the faulty IAC valve with a new one is often the first instinct for many. However, you must first try to repair it. Repairing an idle control valve is simple as you only need to do a little cleaning.

You can easily access the IAC valve to clean it. Ensure to use a good degreaser for cleaning and a wire brush to scrub the ends. Cleaning the valve will not make them as good as new valves. However, it’ll improve their functioning by several notches.

Replacing an IAC valve

If cleaning the valve doesn’t do any good, you need to replace them. Thus finally, in our guide on malfunctioning idle air control valve symptoms and repair techniques, we will teach you how to replace the valve.

 Following is a step-by-step procedure for replacing an IAC valve.

Step 1: Battery disconnect

Disconnecting the battery is a must whenever you’re dealing with electrical components. If you skip this step, your car’s instruments and components can get damaged due to static charge.

Step 2: Locating the valve

Locating the valve can be a bit tricky. It is usually placed either on or near the intake manifold or the throttle’s body.

Step 3: Disconnecting the wiring harness

The next step involves locating the wiring harness to which the valve is connected. Then, release the valve’s electrical terminal. Furthermore, there is also a tab or a clip for disconnecting. You can use pliers to remove it.

Step 4: Removing the retaining bolts

In this step, we will detach the IAC valve by unscrewing each of its bolts. After removing the bolt, you will only have to pull the valve out of its place.

Step 5: Cleaning the seat

After removing the valve, its seat will be visible. The place where you will fix the new valve needs to be cleaned using a throttle body cleaner.

Step 6: Installing the new IAC  valve

Your new valve’s wiring terminals, seat placement, and retaining bolt pattern must be similar to your old valve. Once you’ve verified this, install the new IAC valve into its place. Ensure the bolts are tightened properly. Use a rachet and snug to fit them tightly.

Step 7: Reinstalling the harness

You need to refit the wiring harness to the IAC valve. The terminal and the clip should be connected properly to ensure a secured connection.

Step 8: Reconnecting the battery

We need to reattach the battery to the negative battery cable in this step. Tighten the bolts, so they don’t loosen up when the engine vibrates.

Step 9: Testing the speed

The last step is testing the idle speed. Turn on the engine and note the idle speed. The lowest idle speed should be 550 RPMs, and the highest should be approximately 1000 RPMs.


Apart from knowing an Idle air control valve symptoms and repair techniques when it malfunctions, you must also try learning other similar and extremely useful skills. These skills include inspecting the ignition system, fitting a coil, and installing components such as radiator sealers, spark plugs, and resonators.