How to Stop Rough Idle: The Complete Guide


A rough idle is considered when your vehicle idles is above 800 RPMs, below 800 RPMs, or when it is going up and down. The reason for the rough idle is a clogged idle air control valve that has the task of regulating the air going into the engine at idle and maintaining the idle which should be around 800 RPMs.

The idle air control valve can be stuck in an open or closed position. Either way, it will disrupt the normal idle of the engine. In this article, I will be showing you how to clean the idle air control valve at home and stop the rough idle.

What Does An Idle Air Control Valve Do?

The IACV is responsible for managing the engine’s idle speed. It does this by regulating the amount of air that bypasses the throttle valve when the vehicle is idling. The IACV is controlled by the engine computer, which takes into account various factors such as engine temperature and loads to determine the appropriate idle speed.

The throttle body regulates the air that goes into the engine. If you give your car a little bit of gas, the throttle plate opens up accordingly and allows air to go into the engine. But how does air goes into the engine when you aren’t pressing the gas pedal? This is where the idle air control valve (IAC) comes into play.

There is a hole before the throttle plate that is connected to the idle air control valve which allows air to travel from in front of the throttle plate and into the idle air control valve and into the engine. It feeds the engine enough air to keep the engine idling at the proper RPM.

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A clogged idle air control valve will cause a rough idle. The IACV allows air to bypass the throttle when the engine is idling, so if it’s clogged, the engine can’t get enough air and will stall. In some cases, a clogged IACV can also cause the engine to run rough or misfire. If your IACV is clogged, it’s important to have it cleaned or replaced as soon as possible. Otherwise, you could end up stranded with a dead engine.

Most experts recommend cleaning your IACV every 30,000 miles or so. However, if you live in a dusty area or do a lot of off-roading, you may need to clean it more often. If your engine starts stalling or running rough, it’s also a good idea to check the IACV and see if it needs to be cleaned.

How to Stop Rough Idle: The Complete Guide

If your vehicle is idling rough or stalls frequently, it could be due to a problem with the idle air control valve. When the idle air control valve gets clogged, it can cause the engine to stall or run rough at idle. So, before you take your vehicle to the mechanic shop to replace it, here is how to stop a rough idle by cleaning the idle air control valve:

1. Required items for the task

  • Safety glasses
  • Gloves
  • Carburetor or intake throttle body cleaner (anything that can dissolve carbon deposits)
  • A toothbrush or a pipe cleaner (anything that can get the carbon agitated)
  • 12-millimeter socket
  • Optional: New gasket (comes in handy when reinstalling the IAC to make sure you won’t have any air leaks)

2. Locate the idle air control valve

How to Stop Rough Idle

In your mission to stop the rough idle, the first step is to locate the IAC. The idle air control valve is located in the throttle body of the engine. It is a small, round, metal valve that controls the amount of air that flows into the engine when the vehicle is idling. The idle air control valve is controlled by the computer and opens and closes to maintain the correct idle speed.

Find the air filter box where the air filter sits and then follow the intake tubing to the throttle body and it will take you to the idle air control valve.

In most vehicles, the idle air control valve is located on or near the throttle body. To find it, look for a small, round metal valve with a vacuum hose attached to it. The vacuum hose should be connected to one of the ports on the throttle body. In some vehicles, the idle air control valve may be located on the side of the engine near the throttle body. If you can’t find it, consult your vehicle’s owner’s manual or service manual for its location.

3. Remove the idle air control valve

How to Stop Rough Idle

The idle air control valve has an electrical connector and two bolts that hold the IAC in place. So, first, unplug the electrical connector from the valve and place it safely aside. Then, grab the 12-millimeter socket and remove the two bolts. The most important thing that you need to look after here is not to drop the bolts and lose them. Once you loosen them, unscrew them using your hand just to be sure.

Once the two bolts are removed and the electrical connector is disconnected, the idle air control valve is ready to be removed. When you do that, make sure to tape off the opening that goes into the intake so no dirt or debris gets into your engine while you clean the IAC.

4. Clean the idle air control valve

How to Stop Rough Idle

While holding the idle air control valve, you will notice two openings in which the air travels from the atmosphere and into the engine. If you look closely inside the two openings, you will notice a spring. When the vehicle idles and the engine computer needs more air or it has enough air, the spring will either open or close therefore allowing or closing the air passage. The main problem occurs when that spring gets carbon deposits buildup and gets stuck in an open or closed position.

The most important thing when cleaning an idle air control valve is to always keep the motor facing upwards. This is because when you spray the cleaner, you don’t want the liquid to go down the shaft and into the motor because it will damage it.

With your gloves and safety glasses on, position the idle air control valve in your left hand with the motor facing upwards. With the right hand, spray the carb cleaner into the openings of the IAC. Use the pressure from the spray to knock loose any of the carbon deposits and force them out of the valve.

Next, grab a toothbrush or a pipe cleaner and thoroughly clean the IAC. Poke around on the top opening, clean the surface where the gasket sits, then move on to the bottom opening as well. Try to agitate as much of the carbon deposits as possible. Then, give it one more spray to flush everything out.

5. Reinstall the idle air control valve

Once your idle air control valve is nice and clean, it is time to reinstall it. I mentioned above that you can replace the gasket. Personally, I would inspect the gasket and see if it has cracks or any damage. If so, it is best if you replace it. However, if the gasket is in perfect condition, you can reuse it. Align the old gasket and place the idle air control valve on top of it. Install the two 12-millimeter bolts and then snap the electrical connector back on.

6. Start your vehicle

When you start your vehicle, the RPMs will probably be above 1000 or so. That is fine because the vehicle’s engine is cold. However, after running for a minute or so, the RPMs should drop and be set to about 800 RPMs. If this is the case, you have successfully cleaned a clogged IAC and stopped a rough idle.

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Hi there. I am a certified Automotive Service Excellence (ASE) mechanic since 2018 and a car detailer for 10 years.

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