Maintenance Tips, Tricks And Hacks For Your Vehicle

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.

Key Takeaway

  • 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.
  • Rough idle in cars is primarily caused by factors such as air and fuel mixture imbalances, ignition system issues, or mechanical problems within the engine.
  • Common signs of rough idle in cars include fluctuating or unstable engine RPM, noticeable vibrations or shaking, and an overall unsteady engine operation at idle.

What Is Rough Idle?

Rough idle is a condition where your car’s engine runs unevenly or ‘rough’ while your vehicle is stationary or not in motion.

This could be noticeable through the vibration or shaking of the car, irregular engine sounds, or a feeling that the engine is sputtering or missing its regular rhythm.

Rough idling can be caused by a variety of issues such as dirty fuel injectors, old spark plugs, incorrect idle speed, vacuum leaks, or problems with the air-fuel mixture.

It’s important to address rough idling, as it can lead to poor fuel efficiency, reduced power, and potentially serious engine damage over time.

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.

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 says Berryman Products.

What Causes Rough Idle In Cars

  • Dirty or clogged air filter
  • Vacuum leaks in the intake system
  • Malfunctioning idle air control valve
  • Faulty spark plugs or ignition system
  • Dirty or clogged throttle body
  • Fuel system issues, such as a clogged fuel filter
  • EGR (Exhaust Gas Recirculation) system problems
  • Mass airflow sensor malfunction
  • Problems with the PCV (Positive Crankcase Ventilation) system
  • Engine misfires
  • Low fuel pressure or a failing fuel pump
  • Incorrect engine timing
  • Exhaust system restrictions or leaks
  • Bad oxygen sensor(s)
  • Low engine compression
  • Aging or worn-out engine components

Symptoms of Rough Idle

  • Fluctuating or unstable engine RPM (revolutions per minute) at idle.
  • Noticeable vibrations or shaking of the vehicle.
  • Engine may stall or hesitate when idling.
  • Unusual noises, such as knocking or misfiring, when the engine is at idle.
  • Poor fuel efficiency.
  • Increased emissions and the potential for a check engine light to illuminate on the dashboard.
  • Rough or uneven engine operation that can be felt through the steering wheel or while sitting in the car.
  • Reduced overall engine performance, including sluggish acceleration and response.

Is It OK To Drive With a Rough Idle?

Driving with a rough idle is generally not recommended. While it might be possible to drive for short distances with a rough idle, it’s not ideal for several reasons.

A rough idle can be a symptom of underlying issues in the engine, which, if left unattended, could worsen over time and lead to more significant and costly repairs.

Additionally, a rough idle can negatively affect fuel efficiency and emissions, potentially causing long-term damage to your vehicle’s catalytic converter.

Moreover, driving with a rough idle can compromise safety and overall vehicle performance, as it may lead to engine stalling or hesitation when you need power the most, such as during acceleration or while navigating traffic.

How Much Does It Cost To Fix Rough Idle?

Minor issues such as a dirty air filter or spark plug replacement can be relatively inexpensive, typically ranging from $50 to $200, including parts and labor.

However, if the rough idle is due to more complex problems like a faulty idle air control valve, vacuum leaks, or engine misfires, the cost can escalate significantly.

Repairs for these issues can range from $200 to over $1,000 or more, depending on the extent of the damage and the parts that need replacement.


Q: How can a dirty air filter cause a rough idle?

A: A dirty air filter can restrict the airflow into the engine, leading to an imbalance in the fuel and air mixture. This can result in an erratic idle and poor engine performance.

Q: Can faulty spark plugs cause a rough idle?

A: Yes, worn or damaged spark plugs can cause your engine to misfire, resulting in a rough idle. It is important to regularly check and replace spark plugs as needed to maintain smooth engine operation.

Q: What role does a clogged fuel injector play in rough idle?

A: A clogged fuel injector can disrupt the proper fuel flow into the combustion chamber, causing the engine to run rough at idle. Cleaning or replacing the fuel injector can help restore smooth idle operation.

Q: How does a vacuum leak contribute to rough idle?

A: A vacuum leak allows unmetered air to enter the engine, upsetting the air-fuel ratio. This can result in a rough idle, as the engine receives too much air and not enough fuel.

Q: What is the function of an idle air control valve?

A: The idle air control valve regulates the amount of air that enters the engine during idle. A malfunctioning idle air control valve can cause a rough idle as it fails to maintain the proper idle speed.

Q: How can carbon deposits in the throttle body affect idle?

A: Carbon deposits can accumulate in the throttle body over time, restricting the airflow into the engine. This can disrupt the air-fuel mixture and lead to rough idling.

Q: What is the significance of a check engine light in relation to rough idle?

A: A check engine light can indicate various engine problems, including issues that can cause a rough idle. If your check engine light is on, it is recommended to have your vehicle diagnosed by a professional to determine the exact cause of the rough idle.

Q: How can I fix engine idle problems in my car?

A: Fixing engine idle problems depends on the specific cause. It may involve cleaning or replacing the air filter, spark plugs, fuel injector, throttle body, or idle air control valve. It is best to consult a mechanic for a proper diagnosis and recommended repairs.

In Conclusion

In conclusion, addressing a rough idle in your vehicle is crucial not only for a smoother driving experience but also for the health and longevity of your engine.

By diagnosing and resolving issues related to air intake, vacuum leaks, ignition components, and more, you can regain control of your engine’s idle and enjoy a more efficient and reliable ride.



Vide Polowenski, Senior Mechanic

The information in this article is current and up-to-date in accordance with the latest mechanic SOPs.

Please take the time to leave a comment if this article has helped you in any way, you need additional help, or you have a suggestion.

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