Idle Air Control Valve (Function, Bad Symptoms & Replacement Cost)


In this article we are going to explain about the basic function, working principle, bad symptoms and replacement cost of idle air control valve in your vehicle. Here we go…

Idle Air Control Valve Function

When the engine is running but the vehicle is not moving, this means the engine is idle. During this time, the number of revolutions per minute inside the engine will change. The idle air control valve is responsible for managing the engine idle speed. The valve is a major management component of the engine which will either decrease or increase the number of revolutions per minute, depending on what the current operating conditions call for. The valve is connected to the throttle body next to the intake manifold. The engine control unit is what manages the function of the valve. Based on the information it receives like engine load and temperature, it will change the speed of the idle accordingly.

Bad Idle Air Control Valve Symptoms

When you have a bad idle air control valve in your car, there are several problems and symptoms that will present themselves. If you don’t get the valve replaced immediately, your car will become undrivable. Below are the top 5 symptoms of a bad idle air control valve which you will easily notice.

1. Intermittent Idle Speed

Since the idle air control valve is supposed to manage the idle speed of the engine, a bad valve will certainly throw that out of whack. It will cause the idle speed to randomly fluctuate to different speeds rather than stay at one constant speed. The idle speed may be too high at one moment and then too low at other moments. You will clearly notice this idle speed changing by simply looking at the tachometer on the dashboard.

2. Check Engine Warning Light

Whenever there is the smallest problem or issue with anything connected to the engine, it will cause the central computer to activate the check engine warning light on the dashboard. A bad idle air control valve could certainly be one reason for this to happen. If the number of revolutions per minute seems peculiar to the engine control unit, it will let you know by activating the warning light. Of course, there could be a whole list of other reasons for the warning light to come on too. In any case, you should take your vehicle to the auto shop to get it checked out at once.

3. Rough Idling

A normal healthy idle air control valve will provide smooth idling in your vehicle. But if the valve goes bad for any reason, the idling will go from smooth to rough. A rough idle will result in intense vibrations forming whenever your vehicle is stopped with the engine running. Since less air will be going into the engine during its idle state, the car will react by shaking profusely.

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4. Engine Stalling

If you experience engine stalling from a bad idle air control valve, then you won’t be able to drive your vehicle at all. As soon as you start your car, the idle air control valve will immediately malfunction. If you happen to be away from home and this happens, the stalling will happen every couple of minutes in the beginning. You should be able to make it to the nearest mechanic in time before the engine stalls completely.

5. Load Causes Stalling

Sometimes the engine stalling will happen on its own while other times, increasing the load on the engine will cause it to stall. For example, if you turn on your heater or air conditioner when you have a bad idle air control valve, then your engine will probably stall immediately afterward. The steering wheel might also feel like it’s being dragged to one side too. To temporarily fix this problem, just turn off your heater or air conditioner to reduce the load. Then let the engine cool for a couple of minutes.

Idle Air Control Valve Replacement Cost

If the voltmeter showed a reading outside of the normal range, then you need to purchase a new idle air control valve. Unless you know a lot about auto repair, you’ll need to pay a mechanic to perform the replacement job too. That means you’ll need to pay both parts and labor costs.

The average replacement cost of an idle air control valve is between $120 and $500. The parts could cost anywhere from $45 to more than $400, while the labor is only around $70. Of course, the labor cost really depends on the hourly rate of the mechanic. Since this job should not take more than 1 hour to perform, don’t expect the cost to be too high. Certain vehicles are more complicated to work with than others, so that is a factor too.

How Idle Air Control Valve Work

Engine speed refers to the number of revolutions it makes per minute. This is commonly referred to as revolutions per minute, or RPM. The current operating conditions of your vehicle will cause the idle air control valve to either increase or decrease the RPM in your engine. For instance, if your vehicle has a heavy load or it is heating up too quickly, then the idle air control valve will adjust the RPM by increasing or decreasing it; respectively. This will allow the engine to handle the heavier load or cool down in each case.

The engine control unit is responsible for managing the idle air control valve. When this central computer receives information about the temperature and load of the engine, it uses this information to make the proper adjustments to the idle air control valve. That way, the valve will regulate the engine RPM properly based on the information relayed from the computer.



  1. Victor Fowler 2 February, 2019 at 15:06 Reply

    It’s exactly what this article addresses, cars may be different in many ways but they all still work on the same basic principals. Replacing the IAC valve is easy and if your not sure simply go on YouTube and you’re sure to find someone who has made an instructional video on how to do it. It’s how I just replaced the clutch in my car, and successfully to I might add without ever having done one before. All for less than 1/10th of what a shop would have charged me thanks to ebay where I got the entire O.E.M. clutch kit FOR $60. So order that part and retrive the knowledge you will need and as a by-product of such your accomplishment will garner you some confidence, and good luck to you sir.

  2. bennie 13 February, 2019 at 21:22 Reply

    my 01 ford focus 2.0 I can undo the battery and re kook it to make the iac valve work but after about 20 miles it dose it aging could the iac valve have a short in it

    • Roro 11 March, 2019 at 06:59 Reply

      I have a 2003 Ford Ranger and this happens to me too. My idle will randomly get low, and get to below 500 like the engine will stall. So I turn engine off and unhook the neg. battery cable & re-hook it, then restart and do idle relearn procedure…and it idles good again. But then after a few hundred miles it will start to idle low again. I replaced my IAC valve 20,000 miles ago w/ OEM Motorcraft. Maybe my truck would do better with an aftermarket IAC valve…I’m so confused about this issue. Any advice appreciated.

  3. JOSE MANUEL VEGA 19 February, 2019 at 23:51 Reply

    I have a Toyota Sienna 2001. I would like to know why or how IAC valve affects the brake booster in my car. I had the booster replaced two weeks ago, but the brake pedal seems to get hard and doesn’t brake correctly. Thank you for your help.

  4. Chrystie Galbari 7 March, 2019 at 01:38 Reply

    I had a bad AIC valve. I changed it & not the car will not start at all! What could be the problem

  5. alec 11 March, 2019 at 23:48 Reply

    I have a 2012 ford escape and at idle my car almost stalled, rpm went way below 500, but then picked back up. I think it is spark plugs needs to be changes but could it be AIC valve?

  6. Bulisa 17 April, 2019 at 15:53 Reply

    Hi my vw tenacity 1,4i the car doesnt move whn it is cold if i try to rev t it gives me a low idle till the tempreture rises service is up to date wht could be the problem

  7. Dumb Nuts 1 August, 2019 at 19:19 Reply

    Hi, I’m a dumbass who thinks this is a free “diagnose my problem for me” page. I’m too lazy to do any research myself, so please do it for me and then give me step-by-step instructions on how to fix the problem. P.S. I don’t have any tools and have trouble concentrating for more than 30 seconds at a time. Thanks.

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