What's an IAC on a Car and How Does It Work?

The IAC valve in your vehicle is a sensor and valve in one body and it helps you get the proper idle speed at any conditions. This is the simple mechanism that is usually used in fuel-injected vehicles with standard throttle bodies. Modern cars more often now use complicated sensor systems to adjust the idle speed for different conditions.

Engine idling problems highlights

• Level of urgency:Low
• DIY inspection:Possible but may be complicated
• DIY repair:Sometimes, possible
• Cost of repair:$150 - $600
• Can you drive?Yes
• Commonreasons:IAC valve, throttle position sensor, MAF sensor, carb problems, fuel pressure issues, air supply problems
• Ways to fix:Adjusting the system or replacing the faulty sensor or another part thatis diagnosedto be bad

Where is the IAC valve located?

This valve is a black plastic unit located directly in the throttle body. It's inserted into the body and is usually fastened with two small bolts. Also, it has a clip with several wires connected to it. There are different types and shapes of these valves. Also, they work in different ways. Some of them are small motors while others are fully electric and pretty simple.

The working part of the IAC valve is usually made of metal and has a conical shape. This part is pressed towards the conical part of the throttle body and lets or doesn't let some small portion of air into the combustion chamber when needed.

Here's how this works:

• the idle air control valve gets information from other sensors, mainly it gets the info about the idle speed of the engine;
• usually, it's closed, especially when the engine is running higher than in idle, so the valve rests when you drive;
• also, the valve gets an electrical connection which powers its electrical motor and helps it move the conical part back and forth;
• when the engine idle goes down, the idle air control valve opens a little to compensate for the loss of RPM;
• this allows your engine to work at the proper idle speed, not stall, and overall work smoothly and without problems when idling;
• when you step on the gas pedal, the idle air control valve closes and allows you to fully control the air supply by moving the throttle.

The idle air control valve gets different information from the throttle position sensor, ECU, and other units of your car. It allows the valve to make proper solutions for opening or closing. But this unit is not eternal and it can fail sometimes. Probably, this is how you got onto this page - your IAC valve was broken and now you want to know how it works.

Well, although there is nothing you can do when the valve is broken but replace it, I will tell you about the symptoms of a bad valve, issues it can lead to, and also ways to prevent problems with the system.

What are the symptoms of a bad IAC valve?

When the idle speed of your engine is unusual, you may immediately think about the IAC valve. But things may be not so easy to locate because the high or low RPM may also be the consequence of different problems - throttle body issues, throttle position sensor, ECU glitch, etc.

So, you should know about the symptoms that tell you exactly about the problems with the idle air control valve.

Here they are:

• Low RPM - it's almost always connected with the stuck closed IAC valve.
• High but stable RPM - if your engine stays at a high RPM that doesn't fluctuate, this also tells you about the IAC problems.
• Check engine light - it may or may not illuminate in different cars, but it's always worth paying attention to.
• P0505 error code - if your ECU saves the P0505 code, it always shows the problems with the IAC system.

Also, you should be careful because very often the problems with the throttle position sensor show the same symptoms and this may be quite misleading. Before replacing the valve, you should be sure this is the thing that causes problems.

One good thing is that the IAC valve doesn't usually cost a lot of money. You can buy a new one (maybe even aftermarket) to install it and check whether something changes. You should also check the condition of the throttle body. Maybe, it's worn out and lets air go into the combustion chamber without the IAC valve knowing that.

How can you repair the IAC problem?

There are different situations and you should first locate the problem. It may be the issue with some other part of your car, not the IAC valve. But if you are sure the problem is in the IAC system, you should try and solve the problem.

Here's what you can do:

1) Check the connection

The connection clip on the IAC valve may be the culprit of the problem. You can check it, clean it, or just take it off and then on again.

2) Take the valve off

Look at the valve. If its working part is damaged, you should just install the new one. Check if there are contaminants that can change the way it works.

3) Clean the throttle body

The place where the IAC valve seats may often be rich in dirt and different deposits. Use carb cleaner or any other product to clean this place.

4) Install the new valve

If you are sure that the problem is caused by the bad valve, just get the new one. Install it and try starting the car.

5) Check if everything works well

If the symptoms are still there, you may need to reset the IAC valve. In different vehicles, it's done in various ways. Also, the IAC system requires adjustment, so you may need to drive a couple of miles.

Can you still drive if the IAC valve is broken?

Many drivers are afraid to even start their cars when they understand that the IAC valve is not working. But usually, this is quite safe and you shouldn't call roadside assistance or a tow truck to help you solve the problem.

Whenever you press the gas pedal, the idle air control valve stops working. It will only kick in when the engine is idling and will help you maintain the needed idle speed. So, it's completely safe to drive your car even if the idle air control valve is destroyed. The only bad effect you can get is a little extra air coming into the combustion chamber, so the car will work at a higher RPM.

If the idle speed is abnormally high, it doesn't mean that the engine will work poorly when you are driving. Once the throttle opens, the IAC valve doesn't play a big role in how the engine works.

Why do idle air control valves go bad?

To prolong the life of the IAC valve, you need to know why they malfunction. Sometimes, it just happens because of their age or low quality. For example, at 150,000 miles you can expect the OEM IAC valve to be completely worn-out. Also, if you installed the cheap aftermarket part a year ago, you can expect it to be destroyed now.

But there are different things that may kill the IAC valve:

• water damage - if some moisture gets into the air intake in your car, this can quickly kill the IAC system;
• dust and other particles - if your air filter doesn't work well or isn't clean, it may contaminate the throttle body and the IAC valve;
• wrong electrical connection - high or low voltage will most likely kill the valve and it just won't move at all;
• wrong signals from other parts - if the valve gets wrong signals from the ECU and throttle position sensor, it may malfunction and eventually die.

So, there are quite a lot of problems that may kill the IAC valve eventually. You should know about them and prevent these problems from happening in your vehicle if you want to prolong the life of the IAC system.

How to maintain the IAC valve?

It's impossible to hope that the IAC will work for ages if it has poor conditions of operation. To prolong its life, you should do the following:

• regular IAC valve cleaning;
• regular throttle body cleaning;
• air filter replacement sooner than the manufacturer recommends;
• avoiding driving with a dying 12V battery;
• addressing all the minor problems with the engine immediately.

Final thoughts

You should know about the work of the IAC valve if you own a vehicle with a fuel-injected engine. This small part can get on your nerves and spoil your mood if you don't know about the symptoms of its problems and possible solutions. In this article, I tried to briefly describe everything you need to know about the IAC valve and its functioning. If you still have any questions, please write them in the comments below!