6 Symptoms of A Bad Idle Air Control (IAC) Valve

A vehicle is composed of so many parts that it gets overwhelming to talk about it. The idle air control valve is one of the not-so-known parts of a vehicle that does not get discussed often.


The most common symptoms of a bad idle air control (IAC) valve are a check engine light and randomly fluctuating idle speed. We discourage driving with a bad idle air control valve as it can lead to engine stalling, which can be incredibly dangerous.

We’ll additionally cover the following topics:

  • The best device to test it
  • How to fix it

Usually, the spotlight is on a high-level understanding of an engine rather than the individual parts that make it. We’ll dig into each of the symptoms of a bad idle air control valve.

Table of Contents

When riding a car, it does not run at the same speed all the time. Depending on several external elements, such as traffic or weather, it goes fast or slow. A car that is not moving is idle. It means it will not make any sense if the engine behaves similarly when the car is moving.

Manufacturers invented it to address this behavior.

What are the 6 symptoms of a bad idle air control valve to look out for?

Just like any other mechanical component, it has the possibility of breaking down on occasion. If it goes bad after several years of service, it is not an indicator of poor quality. Still, rather it is common to happen in mechanical components.

What makes matters worse is that even when your vehicle acts up, you might not immediately suspect something wrong with this little-known part. You need to take a series of steps to determine which specific component is at fault. Below are six idle air control valve symptoms that usually show when it goes bad.

If you want to take a closer look, look next to the intake manifold where the valve is usually located.

Here are some of the symptoms we’ll take a closer look at:

  • Check engine light
  • Idle speed fluctuating
  • Rougher idle engine sound
  • A vibrating feeling

1. Did the check engine light come on?

The check engine light indicates that your vehicle has one or more issues. However, having it come on does not necessarily mean an issue.

It comes on even if the vehicle does not have any problems, but that is rarely the case. The computer systems are sending a signal that something is wrong. As the owner, you should act and do everything in your power to find the failure.

To be on the safer side of things, check for any possible issues with the vehicle when you see the light on. The problem could either be the valve or something else.

So, you might be wondering what causes the check engine light to switch on. Whenever the control unit picks up an irregular pattern with how the engine behaves while idle, the check light gets switched on.

Check the vehicle for possible issues. If you are still unsure if the issue is the valve that has gone bad, read on.

See if there are any signs of the other possible symptoms below. Suppose the check engine light is on and combined with the other symptoms listed below. You are likely experiencing a problem with the valve.

Make sure to get it checked out to avoid performance issues.

2. Does the idle speed randomly fluctuate?

Idle air control valve

The idle speed of a vehicle is usually consistent. The idle speed is very much dependent on several external factors such as engine temperature and load. Given a particular condition, it should have consistent idle speed while it is in that condition.

Your engine is idling, and your RPM runs at 800 revolutions per minute. If it stays consistently at 800 RPM, you likely do not have any issues with your valve.

The problem begins if you notice your idle speed jumping all over the place. For example, your engine is idling and is running at 1000 RPM. A few minutes later, it goes down to 800 RPM and then to 900 RPM.

When your engine is left idling, and the inconsistency in RPM does not go away, it is a clear sign that there is an issue. Reach out to a professional as soon as possible. Do not take it for granted, as it may lead to more complicated issues when left unattended.

Suppose you own a professional garage and get a lot of waste oil as a consequence. We encourage you to take a look at these garage waste oil heaters that might save you a lot of money.

3. Does the engine sound rougher on idle?

Vehicles manufactured years ago will have an outdated engine control unit that cannot compensate for problems the component has. As the technology behind the control unit got better, it reached a point at which it could make up for shortcomings with this crucial component.

4. Are you experiencing a vibrating feeling in the car?

Idle air control valve from the top

When your vehicle’s engine sounds off on idle, the valve may be faulty. In most cases, a bad one will also produce a vibrating effect throughout the vehicle.

If this is the case, you may need to have a professional check it as soon as possible. Look out for vibrations and their source! Failure to do so could be dangerous.

So how do you know if it is working as expected and like it’s supposed to? You can determine this with the sound your engine is producing. An idle engine with minimal and unvarying sound is a sign that it is running smoothly.

5. Does the engine stall frequently?

It happens when it stops abruptly and suddenly stops operating. Experiencing a stall does not necessarily mean your engine is completely dead and won’t restart. It could die, then come back up after a few restart attempts.

One of the causes of a stall is a faulty valve. The engine will stall when it does not get enough air supply while it is idle. Another possible reason for the engine to stall is when the control unit cannot compensate for the valve’s issues.

Like any other mechanical issue, the engine stall will occasionally occur during the first few times. If you do not call for a professional to check the problem, it will occur more frequently.

6. Do you experience vehicle backfires?

If you see flames coming out from the vehicle’s exhaust pipe, that is known as a vehicle backfire. It backfires when combustion happens outside the combustion cylinders.

When it backfires, it could be another possible symptom. However, it is also consequential to know that it could indicate a completely different kind of issue. 

Accelerate your vehicle to determine if the backfires you are experiencing are due to this component has gone bad. Let it decelerate and observe if the vehicle twitches. 

Once you have done that, check the exhaust pipe for leaks. It is usually found at the vehicle’s rear. Suppose the vehicle twitches as it decelerates and fuel leaks from the exhaust pipe. It is most likely a problem related to the idle air control valve.

You should know contaminants can build up from the constant airflow to the part is exposed to.

Cheap diagnostics device

There’s a way to figure out what the error in the dashboard means, and you don’t have to be a technician or take it to a repair shop just yet for an expensive procedure.

Here’s one we recommend, especially if your car is showing a check engine light.

Item Weight‎9.6 ounces
Live Data Stream/EVAP/VIN
Package Dimensions‎9.17 x 6.34 x 1.42 inches
Screen Size128×64 Back-lit LCD


  • It’s one of the best value diagnostics devices on the market.
  • More than 35,000 people have left reviews.
  • We believe all cars should have this diagnostics device in the trunk.
  • It can help erase codes, too.


  • You can get more functionality by going higher-end.
  • Some people have not managed to clear error codes with it.
  • A user tested it on a ’96 model that it didn’t work on, but it should work on cars newer than that.
Cheap car diagnostics device
If you suspect you have problems with your car, we encourage you to get one of these fancy little IAC sensors. With thousands of positive reviews, this product will save you more money in car repairs than you could ever imagine.

What does an idle air control valve do?

The idle air control valve is otherwise known as an idle air control actuator. It handles the rotational speed of an idle engine.

What is even more interesting is that the idle speed is not the same all the time. Several factors such as load to the electrical system and temperature contribute to how slow or fast the idle speed is.

What happens when it goes bad?

Nissan maxima 2001 IAC valve

The idle air control valve is responsible for controlling the RPM when idle. It essentially puts the engine in a relaxed state whenever the power is not needed. A vacuum leak may also cause low RPMs.

When the idle air control valve goes bad, the engine will stall. It means it may abruptly stop working. The effects usually gradually worsen in time. It may start with one to two stalls in a week and may worsen to three or more per day. Are you experiencing engine stalling on the road?

Give your engine a break by switching off the air conditioner.

Here’s a real-world example. You are at a stoplight, and there are still 60 seconds left at the stop sign. If you lift your foot from the pedal, your engine will go on idle. If you have a bad IAC valve, it may abruptly stop working instead of going on idle.

To avoid any complications, consult a professional mechanic as soon as you experience at least one of the six symptoms. Find out what the symptoms are of a bad IAC valve. Doing so should save you from the possibility of spending more money.

Can you drive anyway?

Yes, you can still drive with a bad idle air control valve. However, the more pressing question is should you drive a car with a bad one?

Driving with a bad component is not advisable, especially not this one. A bad valve will cause your engine to stall, detrimental to your and your passenger’s safety.

It’s also important to know that a bad one could lead your vehicle to fail an emissions test. Park your car and figure out what your next move is to avoid full on failure.

How do I reset it?

There are a few reasons why you need to reset the valve. One common reason is the need to recalibrate it. Another reason to reset it is to make sure that the check engine light is not on by mistake.

Performing a reset is easy and takes a maximum of one minute. First, slightly press the accelerator pedal just before ignition.

Then ignite your engine and leave it running for five seconds. Once that has passed, switch off the engine and wait for about ten seconds. Lastly, ignite your engine again and check if it is idling normally.

Suppose you have done the reset and are still facing issues with it. In that case, it is best to consult a mechanic for professional advice.

Is it stuck open?

If stuck open, it will operate as expected once it reaches an optimal RPM. When the engine starts from a cold state, it may shut down once a small puff of smoke goes out of the exhaust pipe. It is the result of an obstructed component. 

Hopefully, this article has given you a better idea of how to deal with an engine showing symptoms that need to be addressed. That pesky engine light may be an indication of system errors. It could also be that the IAC valve is starting to act up.

You may test it in various ways. You can even have it cleaned. It’s important to know that there comes a time when a replacement is probably inevitable. However, if you’re cleaning it, make sure the throttle position sensor stays in place.

Here is a list of the cars and manufacturers that seems to have a significant number of bad IAC valve cases. You should particularly be looking for the symptoms with any of these cars:

  • 1998 Dodge Ram
  • Dodge Dakota
  • 2000, 2001, 2002, 2003 Honda Accord
  • 2000 Honda Civic
  • Ford Explorer
  • 1999 Honda Accord
  • Jeep
  • 2003 Chevy Silverado
  • 94 Chevy 1500
  • 2000 Nissan Maxima
  • 4.3 Vortec

Whether you have a Miata P0505, it’s important to find its location and see what is going on.

Can a bad one cause hard starting?

Hitachi New Idle Air Control Valve ABV00

Yes, a faulty valve can cause hard starting and rough idling. Make sure to check it out. As you can see above, most of the reported issues that we were able to find were with older vehicles. You shouldn’t let the fear of such a small component be something that worries you! Replacing it won’t be a major expense.

There will be times when you need to fix up a bad air control valve when the car isn’t idling at its best. That is when you need to do the following.

Have you noticed any of the following symptoms indicating a potentially failing idle air control valve?

  • A vibrating feeling
  • An idle engine sound is rougher
  • The idle speed fluctuates
  • The check engine light coming on.

We will be happy to hear your thoughts

Leave a reply

Passion Plans
Login/Register access is temporary disabled