How to Stop Rough Idle: The Complete Guide

A rough idle is defined as any idle that exceeds 800 RPMs, falls below 800 RPMs, or alternates between them. Usually, this indicates a clogged idle air control valve which regulates engine airflow at idle and keeps your car’s engine at approximately 800 RPMs.

In this article, I’ll show you how to clean your idle air control valve at home and restore the engine idle to its normal state. If your IAC valve is stuck open or closed, it can disrupt normal engine idling.

In order to stop a rough idle, you need to locate the idle air control valve and remove it. Then, using a carburetor or throttle body cleaner, spray the idle air control valve and scrub it with a brush. Just make sure that you don’t spray the electrical connector. Then let the IACV dry completely and reinstall it.

Key Takeaway

How to Stop Rough Idle: The Complete Guide

  • Get a cleaner that can dissolve carbon deposits. A carb cleaner or a throttle cleaner will do the job.
  • Locate the idle air control valve. It is located near the throttle body.
  • Remove the IAC valve by removing the two 12-millimeter bolts and the electrical connector.
  • Clean the idle air control valve with the cleaner. It is best if you soak it overnight. Make sure the electrical connector isn’t getting wet.
  • Dry the IAC valve and install it.
  • Start your vehicle and let it idle for 10 minutes. It is normal if the RPMs are higher than 1000. They will settle back down after 10 minutes.

What Does An Idle Air Control Valve Do?

The IACV is responsible for controlling an engine’s idle speed by controlling how much air bypasses the throttle valve when idle. This function is managed by the engine computer, which takes into account factors like engine temperature and loads when setting an appropriate idle speed.

The throttle body controls the flow of air that enters an engine. As you give your car some throttle, its throttle plate opens and allows air to enter, but how does air get into your engine when you aren’t pressing the gas pedal? That’s where the idle air control valve (IAC)Opens in a new tab. comes into play.

Before the throttle plate, there is an air inlet hole connected to an idle air control valve that allows air from in front of the plate and into this control valve and then into the engine. This air supply helps ensure that your engine stays at proper RPMs while you drive it.

Clogged idle air control valves (IACVs) cause a rough idle. IACVs allow air to bypass the throttle when your engine is idling, so if they become blocked it won’t get enough oxygen and may stall. In some cases, an unclean IACV may also lead to rough running or misfiring of your engine.

If your IACV is clogged, have it cleaned or replaced right away; otherwise, you could end up stuck with an engine that won’t start.

Experts generally recommend cleaning your IACV once every 30,000 miles or so. However, if you live in a dusty area or do a lot of off-roading, cleaning may be necessary more often. Furthermore, if your engine starts stalling or running rough, inspect the IACV to see if it needs cleaning.

How to Stop Rough Idle: The Complete Guide

If your vehicle is idling poorly or stalls frequently, it could be due to an issue with the idle air control valve. When this valve becomes clogged, it can cause your engine to stall or run rough while idle. So before taking your car to a mechanic shop for a replacement, here’s how to stop that rough idle by cleaning out 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

Your mission to eliminate rough idle starts with finding the IAC. Located within the throttle body of an engine, this small, round metal valve regulates air flow into the engine when idling.

It is controlled electronically by your computer and opens and closes according to desired idle speed.

Locate the air filter box where it sits, then follow its intake tubing to the throttle body – this will lead you to an idle air control valve.

Most vehicles have an idle air control valve located near or on the throttle body. To locate it, look for a small round metal valve with a vacuum hose attached that should be connected to one of the ports on the throttle body.

In some vehicles, however, this valve may be located on one side of the engine near where it meets with the throttle body; if unsure, consult your 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 (IAC) has an electrical connector and two bolts that hold it in place. To begin, unplug the electrical connector from the valve and set it aside safely.

Next, grab a 12-millimeter socket and remove both bolts with care; be sure not to drop or lose them! Once loosening begins, use your hand to unscrew them slowly but thoroughly for extra assurance.

Once the bolts and electrical connector have been taken off, it’s time to take out your idle air control valve. Be sure to tape off any opening that goes into your engine intake so no dirt or debris gets into your engine while cleaning the IAC.

4. Clean the idle air control valve

How to Stop Rough Idle

Holding the idle air control valve, you will see two openings where air travels from the atmosphere into the engine. If you look closely inside these openings, you will observe a spring.

When idles occur and either enough air or not enough, this spring opens or closes accordingly, allowing or closing passage for airflow. Unfortunately, carbon deposits buildup can cause this spring to become stuck in either position – open or closed.

When cleaning an idle air control valve, it is essential to always keep the motor facing upwards. Doing so prevents liquid from seeping down into the motor shaft and damaging it.

Don your gloves and safety glasses before positioning the idle air control valve in your left hand with its motor facing upwards. With your right hand, spray carb cleaner into any openings of the IAC using pressure from the spray to knock loose any carbon deposits and push them out with ease.

Next, use a toothbrush or pipe cleaner to thoroughly clean the IAC. Begin at the top opening, wipe down where the gasket sits, then move on to the bottom opening as well. Aim to loosen as many carbon deposits as possible before giving everything one last spray to flush everything out.

5. Reinstall the idle air control valve

Once your idle air control valve is clean and tidy, it’s time to reinstall it. As previously mentioned, you can replace the gasket if desired; however, inspect first for cracks or any damage before doing so. If so, replacing may be best; however if in good condition, reuse it!

Align both pieces of equipment together before installing two 12-millimeter bolts and snapping on an electrical connector afterward.

6. Start your vehicle

When you start your vehicle, its RPMs may be above 1000. That’s normal as the engine is cold. After running for about a minute or so, however, the RPMs should decrease to around 800. If this occurs, then you have successfully cleaned out an IAC blockage and put an end to that annoying rough idle.

Igor Iwanowski

I am a certified Automotive Service Excellence (ASE) mechanic since 2018. I specialize in Brake systems, dashboard warning lights, EGRs, general engine problems, EVAP and Emissions issues.

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