Idle Air Control Valve Stuck Open Symptoms

Ideally, we idle car engines when we start and leave the car to run in park. Most folks call it idling even when the AC and other electronics are running. Whether you switch off all the car electronics, including the AC, or switch them on, you are idling the car as far as you do not step on the gas pedal.

Since you do not depress the accelerator, the engine figures out the ideal air needed to run smoothly and at the lowest RPM possible.

The (IAC) idle air control valve is a crucial part of the throttle body in older car models. It works in harmony with the car computer to determine and allow adequate air into the engine without throttle input.

When a car is in park, the throttle body stays neutral. As a result, the car computer will work with the IAC valve to direct the required air into the engine. The IAC valve will manage air input. Since it is in charge of air management on idle, it’ll project several signs when it goes bad.

In this article, I’ll outline idle air control valve stuck open symptoms you should watch out for. You’ll also learn what causes it to go bad and how to test idle air control valves. Grab a seat while I walk you through all you should know.

what happens if you unplug idle air control valve

Idle air control valve stuck open symptoms.

A stuck-open idle air control valve will project several symptoms to let you know something is wrong. The common signs of a stuck open idle air control valve are the illumination of the check engine light, irregular idling, engine stalling, and fluctuating idle speed.

Check engine light

A common sign of a bad, stuck closed, or stuck open idle air control valve is the illumination of the check engine light on the dashboard. However, don’t point accusing fingers at the IAC valve because the check engine light appeared on the dashboard. Several other factors can trigger the warning light.

Scan the vehicle with an OBD-II scanner to pull the root cause of the problem. If the car registers error code P0505, there’s a problem with the IAC valve. It could be the IAC valve is not closing.

Rough idle

The IAC valve is supposed to manage air input and keep the engine running smoothly. If you are wondering what happens when the idle air control (IAC) valve goes bad, the short answer is the engine will run rough. You temporarily resolve the problem by turning off some car electronics like the radio and the air conditioner. But in a real sense, you are not fixing the problem – you are only hiding it.

Here’s what you should know; if the rough idling results from a stuck open IAC valve, you will have rough idle, but it shouldn’t come with other serious issues. If there’s a misfire, you likely have bigger engine issues that need attention, even if the idle air control valve is stuck open.

Fluctuating RPM

I explained earlier that the idle air control valve (IAC) keeps the engine running smoothly. If stuck open or closed, it’ll interrupt the smooth running of the engine, making the RPM fluctuate on idle. So, if you are asking what happens if you unplug IAC valve or if the idle air control valve is stuck open, the RPM will fluctuate, especially on idle.

Kindly note that the engine will fluctuate more when you switch on car accessories because the engine won’t adjust to the change in load due to a bad or no IAC valve.

Engine stalling

A damaged or stuck open idle air control valve (IAC) won’t respond to all conditions. In some situations, you will not notice any problem, and the engine may stall in other cases. Similarly, an idle air control valve stuck closed will cause engine stalling. However, it’ll be unfair if I fail to tell you that several other factors can cause an engine to stall out.

how to clean idle air control valve without removing

What causes idle air control valve to go bad

There are two common reasons for an idle air control valve to fail. An IAC can become faulty by clogging or failing.

Clogged IAC

Since air flows through the idle air control valve, dirt or other contaminants can get into the chamber. The contaminants or dirt could cause blockage or damage to the valve.

Failed solenoid

The idle air control valve has a solenoid inside that receives electric signals when the vehicle is running. If this solenoid fails, it could cause the IAC valve to get stuck open or close.

Now that you have seen the signs and causes of a failed IAC valve, you’ll be asking how do you test an idle air control valve.

How do you test an idle air control valve?

If your vehicle displays any of the symptoms above, you’ll need to troubleshoot the car to know if the IAC valve is bad. Before resetting the valve, you should test it and confirm it is the root cause of your problem.

The simplest way of checking if the IAC valve is damaged is by scanning the vehicle for a related error code. For instance, a P0505 error code stands for idle control system malfunction. If your car powertrain control module logs this error code, you’ll need to clean or replace the IAC valve.

If the engine control module doesn’t throw any error code, you’ll have to monitor how the engine behaves when running on idle.

  • Start the vehicle and allow it to get to the average operating temperature
  • Check the ideal idling RPM for your car and see whether it aligns with the current RPM (You can find this info in your specific owner’s booklet).
  • Switch on the air conditioning system and tone it to the lowest temp
  • The RPM should drop or go up depending on your car model. But it should be between 600 to 1,000 RPM. Disregard the change and see if the RPM is fluctuating on load.

You have a defective idle air control system if the RPM keeps fluctuating. But if the RPM stays steady at a high level, you could have a stuck open IAC, allowing much air into the engine.

What does a bad idle control valve do?

As explained earlier, a bad idle air control valve will cause rough idling, fluctuating RPM, engine stalling, and the illumination of the check engine light on the dashboard. However, several other factors can also cause these issues. So, it’s crucial to diagnose the vehicle before accusing the IAC valve.

How do you reset an idle air control valve?

If you are asking how do I reset my idle air control valve, follow the below steps religiously.

  • Switch the ignition to the ON position
  • Shift the gear selector to park and depress the brake pedal
  • Release the brake pedal and wait for around 5 seconds
  • Return the key to the OFF position and leave the car off for about 10 seconds
  • Start the vehicle and see if it is idling correctly.

Can you clean the idle air control valve?

Yes. Cleaning the idle air control valve periodically will help prevent carbon and other contaminants from clogging the valve, which will negatively affect how the car runs on idle. Though, you have to get a multipurpose cleaner or a product specifically designed for cleaning the IAC valve for better results.

Can I drive with a failing idle air control valve?

You can drive your car with a damaged idle air control valve, but driving with a bad idle air control valve is not recommended. Driving with it can compromise your safety as the car will stall on the road. Plus, you ’ll fail your vehicle emission test since the check engine light will illuminate on the dashboard.

Final Words

The idle air control (IAC) valve controls the air management when the vehicle is idling. It also keeps the vehicle RPM from fluctuating and prevents engine stalling. If the IAC fails, the engine RPM on idle will start acting up.

This article has outlined the idle air control valve stuck open symptoms, how to test it, how to reset it, and how to clean it. If you notice any of the symptoms above, test the valve and confirm it is the leading cause before resetting it. You’ll have to clean or replace the valve if a reset doesn’t fix the problem.



While growing up, I knew I had a thing for car repairs though my parents never wanted me to learn mechanics. I always visit a mechanic garage in my small neighborhood after school. As I grew older, at age 16, I got addicted to anything automotive. My parents had to enroll me in that mechanic garage since giving up was never an option for me. As a dedicated mechanic who got into the industry from an early age, I'm graced with an addiction to diagnosing and rectifying automotive problems with ease.

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