What Happens When The Idle Air Control Valve Goes Bad? Fixing Process & Cost

​You may think that your car starts the engine and keeps working by itself with no help from any component. But that’s not how it works.

For your car to maintain an idle speed and not over-accelerate or stall, it needs the help of an IAC or idle air control valve.

The problem is that this part, like many others, may eventually fail and produce several issues that could damage your car and leave you stranded. But there are a few other problems you could experience when this happens.

Here, we are going to show you the different issues you can experience when the IACV malfunctions and how to fix it.

Take a step further into this article and find out!

What is an Idle Air Control Valve?

In the combustion engine, there’s a part that makes sure the RPM or revolutions per minute do not fall below the right number or go over them. This part is called the IAC or idle air control valve and has the only purpose of keeping the car within the right RPMs when it is idle.

This function of the IACV happens when the car is static. The engine will run at speeds between 900 and 1,100 RPMs. If the vehicle accelerates and goes over 1,100 or decelerates and goes below 900 RPM, then the IAC acts to maintain the right revolutions and prevent the car from stalling or over-working the engine.

This way, the RPMs stay within the ideal range to avoid issues.

The IAC valve attaches to the intake manifold of the car. This means it is a direct part of the breathing system of the engine that keeps it working correctly.

And the only way it can work properly is when it receives information from the engine to keep the acceleration and prevent the speed from being too much or too little in the engine when idle.

So, when the idle air control valve is not doing its job, you will experience a few problems. Here we are going to talk about them.

4 Symptoms of a Bad Idle Air Control Valve

The IAC may be one of the smallest yet essential parts of the engine. When it doesn’t work, you may experience a few issues that will make your car malfunction.

Here are most of these problems;

1. Idle RPMs Go Crazy

When you accelerate the car, the RPM counting will increase. When you put the foot out of the pedal, the RPM will decrease. If the vehicle is in idle, the RPM counting should stay within a normal range. But if the counting goes below or over the ideal revolutions, there’s probably a problem with your IACV.

When this IAC valve malfunctions, then the RPM counting won’t come at its normal range after decelerating. It may stay over 1,100 RPM causing the engine to over-work, or eventually fall below 900 RPM and get to the point of almost stalling.

Sometimes, the IAC valve just makes the RPM counting go crazy, going up and down without control.

This mostly happens when the IAC valve is clogged. However, it may also be a broken or cracked valve, in which case cleaning it alone won’t fix it. You’ll have to replace it.

2. Idle Makes the Car Go Crazy

When the car is in idle, it should stay static and maintain the RPM counting within the range. However, when the AIC does not work correctly, the idling in the car will make it go crazy.

You will probably start feeling how the car shakes, vibrates, the RPM counting will go back and forth, and may even make weird engine noises you don’t expect.

This is called rough idling and happens, almost all the time, due to a bad or clogged IAC valve. Sometimes it could be carbon debris inside the valve, but often it happens that the valve is completely broken or cracked, so air filters inside and the engine malfunctions with it.

It’s recommended to check the IAC as soon as possible if you experience this, as the next time it could stall the engine completely.

3. IAC Overloads and Engine Stalls

When the IACV doesn’t work correctly, the slight increase in load will make it stop working and stall the engine. It needs to keep the ideal air intake into the engine, but when the loads increases and it can handle that much, the IAC will block the entrance of air and the engine will turn off.

This mostly happens when you turn on the AC or the heater. And the car may not even need to be idle. The same happens with the power steering, which also uses electricity and increases the load in the IAC.

Eventually, it will stop working and prevent the engine from working correctly. You may not experience a completely stalled engine, but a significant loss in RPM, which is another clear sign the IAC is faulty.

4. “Check Engine” Warning Light is On

If there’s a problem with the engine, the first thing you may experience will be a “Check Engine” light. It happens due to many things related to the engine. Sometimes, you may not even know it is the IAC until you start checking this part.

However, most of the time it means the IAC is clogged or working deficiently, so you’ll have to check visually & with an OBD II scanner.

How to Fix Bad Idle Air Control Valve?

Now that you know the different things that can happen when the IAC malfunctions, it is time to learn how to fix it.

Take a look at the following tips to know how exactly;

1. Check the IAC 

Before adjusting the IAC valve, you’ll need to check for the exact problem. Here we tell you the ways you can check for a faulty idle air control valve.

OBD Scanner Check

With the OBD II, you’ll be able to receive the error code of the issue. This will tell whether it is the idle air control valve or any other part. To do this, just connect the OBD II to the connector in the driver side, turn the car on, and let the scanner do its work. If the error code is 11, it is the IAC, and it may need replacement. Some vehicles may have different error codes for this problem, so check the manual.

Note: For cars older than 1996, you will need an OBD I scanner instead.

RPM Check

The RPM check is one of the most useful things you can do to check whether the IACV is working correctly or not. You’ll need to do this:

  • Start by taking notes on the idle RPMs of the engine with a regular start. Ignite the car and let it run for a minute or two. Then, when the RPMs start to level off, you can note the engine RPMs. Make sure you have the lowest and the highest RPMs.
  • Now turn the car off and find the Idle Control Motor. This part is typically located close to the engine and intake manifold. It looks like a standard outlet connector or wiring clip and needs no additional effort to disconnect more than just pull force.
  • Some cars will have different Idle Control Motor so you may need to look for the car manual before doing it. We recommend doing this before doing anything else so you can have a better idea of what to do before starting.
  • With the Idle Control Motor detached from the engine, you can now restart the engine. Make sure the ICM is not connected, as you will have to check the RPMs once again but this time without this component.
  • Let the engine run for one or two minutes, so it levels off. Now you can start writing both the high and low RPM levels. Compare them to the ones you wrote earlier with the ICM connected. They should be different.
  • If the idle RPM speeds on the engine are the same when you disconnect the Idle Control Motor, it means it’s not doing its job. This could be either to a malfunctioning ICM or the IACV directly.
  • Now shut off the engine and connect the ICM again. If the RPM readings are once again the same, it undoubtedly means there’s a problem with the ICM. You’ll have to do a resistance & a visual check next to look for any Idle Air Control valve issue.

Resistance Check

Whether you’ve spotted an issue with the RPMs or via OBD scanner, you will have to check the pressure of the IACV to make sure there’s a problem with it. To do this, you will need OHMMETER.

Here’s how:

  • Disconnect the IAC valve. Now connect the ohmmeter to the pins 2 and 3 in the valve.
  • Check the resistance levels. They shouldn’t be different than 10 to 14 OHMs.
  • If the levels are over or below, it means the IAC is not working correctly. Most of the time it means the valve is heavily clogged or broken.

2. Cleaning the IAC Valve

Now that you are familiar with the problem in the IACV, it is time to fix it. And to do this, the primary solution is to clean it thoroughly. Before thinking of a replacement, cleaning will fix your problem if it isn’t too bad.

To do this, you won’t have to spend hours or too much money. Even the most inexperienced car user can do this as long as he does it with care. But before doing anything, make sure you have the following materials:

  • Carbon Cleaner or Throttle Body Cleaner
  • Clean towel cloth
  • Screwdriver
  • Wrench

As soon as you have all these materials, you can proceed with the following steps:

Find the IAC valve

The IACV is usually located close to the throttle body, in the manifold intake. You’ll have to take the intake hose off and unscrew and unclip all the things that attach the IACV valve to the intake manifold. You’ll have to use the screwdriver and the wrench. Make sure to avoid damaging any of the tubes or hoses around.

Remove the IAC

This process will be critical to clean it. However, you’ll have to disconnect all the wires and cables around. Here’s how:

  • Start by disconnecting the battery cable. Then disconnect the electrical plug on the IAC. Now you can detach the IAC by unscrewing the bolts or screws that are typically three or four.
  • The wires you’ll find here will be three. One of r the current, one for grounding, and one that leads to the computer. You’ll have to remove all these wires as well as the screws or bolts holding them together. Remember to make all wires to reassemble this part without issues.
  • Take the gasket out if it is broken or old. You may need to buy a new gasket so be sure to do it before trashing the old one.
  • Now you’ll be ready to remove the whole IAC without a problem.

Clean the IAC and the Throttle Body

Now it is time to get rid of all the carbon and debris inside the valve. You’ll do this using the carbon cleaner or the throttle body cleaner. Follow these steps:

  • Now with the valve out, you can spray the unit with the cleaner you got. Try to remove as much grime, dirt, dust, debris, and carbon from it as possible. Use the cloth to remove the excess and remaining impurities.
  • Remember also to spray the cleaner in the throttle body while the butterfly valve is out.
  • Repeat this process until there’s nothing to clean in the valve. Use the towel cloth to wash everything that’s dripping over the throttle body or the IAC.
  • You may need to drain the excess of cleaning liquid in the valve or throttle body. Use your towel cloth here as well. Make sure everything looks clean before reassembling.

Reassemble Everything

After cleaning everything in the IAC and the throttle body, it is time to let it dry for a few minutes and reconnect. This way you can eventually check that the IACV is now working correctly. Here’s how:

  • Put the IAC back to its original position. The hoses, screws, connectors, and wires should all come back to their original place.
  • Remember to secure everything tightly. Use your screwdriver and wrench to do this. Tighten up the clips and the bolts correctly.
  • Replace the gasket if needed. Remember to install it back correctly to prevent any loose part while the engine is on.
  • Make a last check that everything is in place. Inspect until you see everything connected to the right place and the wires in their respective connectors. Do the same with the battery cables and hoses.
  • After you’ve checked everything, it is now time to close the hood and start the car. The RPM readings and everything else should be working correctly.

If after cleaning the IAC valve you still experience problems with the idle RPM, you may need to replace the IAC. But if the RPM start working correctly, but there’s still a “Check Engine” light in the dashboard, then you will need to check your car further to find the problem.

Idle Air Control Valve Replacement Cost

If you’ve already cleaned the IAC and the problem with the idling of the car keeps going, it’s probable that the valve needs complete replacement.

The process to replace this part is not as hard as replacing other parts, but it is always recommended to let a mechanic do it, as it takes a little more effort and experience than expected.

The cost of a new idle air control valve can be from $50to $500 depending on the model and quality of it. Different cars also use different types of IACV so the cost may vary exponentially.

A mechanic, however, shouldn’t charge more than $100 for replacing this part. So you’ll be seeing a total of about $150 to $600 to replace the IAC completely.

But this is part that rarely fails or needs replacement. So paying for this process will not be something that will bother you, as long as you use the vehicle correctly and prevent any damage to this valve.

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To Conclude,

Remember, though, that this problem could get to the point of stalling the engine and leaving you stranded so at the first sign of a faulty idle air control valve, check for a solution or take it to a mechanic. You won’t like your engine suffering any damage from not wanting to check/replace this part in time.

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