6 Symptoms of A Bad Idle Air Control (IAC) Valve (& Driving With It)

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 about parts of a vehicle that does not get discussed often. Usually, the spotlight is on a high-level understanding of an engine and not on the individual parts that make it, why we are taking this time to actually dig a little bit deeper into some the symptoms of a bad idle air control valve (also sometimes referred to as an IAC valve).

When riding a car, it does not run at the same speed all the time. It goes fast, or it goes slow depending on several external elements such as traffic, terrain, and weather. A car that is not moving is idle, which means it will not make any sense if the engine behaves in the same manner when the car is moving. Manufacturers invented it to address this behavior. If you are interested in other engine related articles, and you own a Thermo King reefer, we have also have an article that goes into detail about its alarm fault codes.

Cheap car diagnostics device
26,614 Reviews
Cheap car diagnostics device
If you suspect you have problems with your car, we encourage you to get one of these fancy little devices. With thousands of positive reviews, this product will save you more money in car repairs than you could ever imagine.

What does it do?

The idle air control valve, otherwise known as an idle air control actuator, handles the rotational speed of an engine that is idle. 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 how fast the idle speed is.

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, but 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 that there is something wrong with this little known part. There is a series of steps that you need to take to determine which specific component is at fault. Below are five idle air control valve symptoms that usually show when it goes bad.

Did the check engine light come on?

The check engine light is an indicator that your vehicle has one or more issues. However, having it come on does not necessarily mean there is an issue. There are times that it comes on even if the vehicle does not have any problems, but that is rarely the case.

To be on the safer side of things, when you see the light on, check for any possible issues with the vehicle. 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 on idle, the check light gets switched on.

After checking the vehicle for possible issues, and you are still unsure if the issue is the valve that has gone bad, read on and see if there are any signs of the other possible symptoms below. If the check engine light is on and combined with the other symptoms listed below, then it is likely you are experiencing a problem with the valve.

Does the idle speed randomly fluctuate?

The idle speed of a vehicle is usually consistent. Although 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.

For example, your engine is idling, and your RPM is running at 800 revolutions per minute. If it stays consistently at 800 RPM, then it is likely you 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, then goes up 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.

If 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.

Does the engine sound rougher on idle?

Vehicles manufactured several years ago will have an outdated engine control unit that is unable to recompense for any problems the component may have. As the technology behind the control unit got better through updates and improvements, it reached a point at which it has become able to make up for any shortcomings with this otherwise crucial component.

Are you experiencing a vibrating feeling in the car?

When the engine of your vehicle 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.

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 engine on idle that has minimal and unvarying sound is a sign that it is running smoothly.

Does the engine stall frequently?

It happens when it stops abruptly and therefore 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 supply of air while it is idle. Another possible reason for the engine to stall is when the control unit is unable to recompense for whatever issues the valve has.

Like any other mechanical issues, 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.

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 be an indication of a completely different kind of issue. 

To determine if the backfires you are experiencing is due to this component having gone bad, accelerate your vehicle. Let it decelerate and observe if the vehicle twitches. 

Once you have done that, check the exhaust pipe, usually found at the rear of the vehicle, for leaking. If the vehicle twitches as it decelerates and fuel is leaking from the exhaust pipe, then it is most likely a problem related to the idle air control valve. Speaking of fuel, you may want to read about fuel transfer tanks.

What happens when it goes bad?

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.

When it goes bad, the engine will stall, which 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 go as worse as three or more per day.

To give a real-world example, you are in a stoplight, and there are still 60 seconds left in the stop sign. Normally, if you lift your foot from the pedal, your engine will go on idle. If you have a bad one, it may abruptly stop working instead of going on idle.

For you to avoid any complications, consult a professional mechanic as soon as you experience at least one of the five symptoms mentioned in what are the symptoms of a bad IAC valve section. Doing so should save you from the possibility of spending more money.

Can you drive with a bad idle air control valve?

Yes, you can still drive with a bad idle air control valve. The more pressing question is, however, should you drive a car with a bad one? No, driving with a bad component is not advisable, especially not this one. A bad valve will cause your engine to stall, which is detrimental to your and your passenger’s safety.

It’s also important to know that a bad one could potentially lead your vehicle to fail an emissions test.

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.

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

How much does it cost to replace?

When it fails, you will have to replace it with a new one. It is up to you if you are going to replace it with one that is the same as the original one or replace it with a third-party brand that is compatible with your engine.

The cost of this component depends on your vehicle’s manufacturer and model. It could cost as low as $70 or as high as $500. Expect that it is going to be cheaper to replace it for vehicles that belong in the budget class level than vehicles that belong in the luxury class level. 

Aside from the cost of the part, you also must factor in the cost of labor for replacing it. The cost of labor will depend on the shop where you are going to have it replaced. In some cases, the cost of labor is free if you purchased the part from the same shop.

How long do they last?

A vehicle whose valve is in excellent condition is a huge factor to consider when determining its condition. A bad one leads to inconsistent idle speeds, which may cause more serious issues in the long run.

It is responsible for keeping your vehicle running when you are at a stoplight. It is also responsible for normalizing the RPM on idle. 

It is such a vital part of a vehicle that it should last as long as its life. However, given how much work it needs to do to keep the vehicle running smoothly, it will eventually reach its end of life, which is normal for mechanical parts.

If the component has reached its end of life does not necessarily mean the vehicle has reached its end of life. Sometimes, it wears out ahead, which means you will have to replace it with a new one if you do not have plans yet to get a new vehicle. 

Is it stuck open?

An idle air control valve that is stuck open 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, which is a result of an obstructed component. 

Hopefully this article has given you a better idea of what you should be doing and how to deal with an engine that may be showing symptoms that need to be addressed. While that pesky engine light may be an indication of greater system errors, it could also be that this little-known component is starting to act up.

While you may test it in various ways, and you can additionally even have it cleaned, it’s important to know that there comes a time when a replacement is probably inevitable.

We took a look at the numbers, and if you are getting a new car to drive in, you should know that there are some people that are seemingly experiencing more issues with this little component. Perhaps it may be because these people are also driving cars that are relatively normal, as we have only taken a look at the absolute numbers when it comes to people talking about this issue, rather than relative, or taken as a percentage of car owners.

While we would have loved to make a more accurate article on the number of relative numbers of people that were experiencing these issues, those numbers were hard to come by.

Here is a list of the cars, brands and manufacturers that we could come by that seemed to have a significant number of cases, why 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

So whether you have a Miata, a P0505, it’s important to find the location of it and see what is going on.

Can a bad one cause hard starting?

Yes, a faulty valve can in fact cause hard starting, and rough idling as well. 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, why you shouldn’t let the fear of such a small component be something that worries you when you are out finding that new truck you have been looking for! Replacing it won’t be a major expense.

While we have you here, there are a bunch of other articles that we would also encourage you to take a look at, assuming you have an interest machinery, why we’d like to draw some attention to our section with plasma cutters and wide belt sanders, or this article on flushing a radiator.

Are you more so interested in getting your garden started? Great, we have an article on getting started with your sansevieria, and how to care for it as well.

Either way, we hope that you learned something new about replacing, cleaning and troubleshooting potential issues with your car that you may not have known about before.

Leave a Comment

Your email address will not be published. Required fields are marked *