(Updated on September 29, 2022)
When the engine is running but the vehicle is not moving, this means the engine is idling. During this time, the number of revolutions per minute (RPM) 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.
How an Idle Air Control Valve Works
Engine speed refers to the number of revolutions it makes per minute. This is commonly referred to as the 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.
Related: How to Test and Clean an Idle Air Control Valve
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 undriveable.
Below are the top 5 symptoms of a bad idle air control valve which you will easily notice.
See Also: Bad Throttle Position Sensor Symptoms
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.
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.
See Also: Causes of a Car That Starts Then Dies Immediately
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 a voltmeter shows 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. 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.
37 thoughts on “5 Symptoms of a Bad Idle Air Control Valve (and Replacement Cost)”
My temperature gauge fluctuates from warm to cold then back to warm. We’ve replaced the temperature sensor a few times and still does it. Any idea what else it could be?
What year, make, and model? If it’s a 1996+, see if an OBD2 scanner will confirm what you’re seeing on the temperature gauge. If it does, it sounds like you may have air in the cooling system. Top off the coolant, then make sure you bleed the cooling system of air properly.
i have a 1995 mercury mystique ive changed coil pack spark plugs and wires after someone washed my engine it wont drive first it wouldnt even start change spark plugs started up but died soon as foot off pedal changed coil pack same thing only this time you can reverse slow but not enough power to go u a lil hill changed spark plug wires car stays on but shakes and sounds real rough but when reverse it barely moves
Could the engine have been flooded? It’s okay to wash the engine bay if you’re careful about avoiding the electronics, but pressure washing is never a good idea because it can force water into a lot of areas it should never go.
Hello,every time after driving 30miles as soon as I reach the stop sign my idling speed rpm goes down to zero and the car stalls and had to start it again and control the idling with clutch and accelerater for it not to stall.plz help
It could be the idle air control valve. You’ll have to do a bit of diagnostic work to determine this for sure.
2011 Buick Regal: I was told my transmission is bad but I have a feeling it’s something else. I don’t have check engine light but it has stalled on me, started right back up. rpm fluctuate in the right under the 1000 range for about 2 minutes after cold start, then settles. Sometimes when I drive I feel like it’s going to go out as I slow down and come to stop sign or light. Any advice would be great and much appreciated!
Why were you told the transmission is bad?
The issue you describe sounds like a vacuum leak or idle air control valve. Not sure, you’ll have to do some testing to pin it down.
Ok, I was told it was bad transmission due to “noticeable vibrations” that’s it, no codes or anything, nothing else was checked. I’ve had the spark plugs, air filter replaced, exhaust manifold and timing chain done! I’m tapped out and don’t want any more costly repairs…but from what I have researched, also suggested iac…hmmm…thanks for your input! I really appreciate it! Ohh there is a rotten egg smell coming from car pipes and some noticeable smoke when I start it up. It’s not a lot but I hadn’t noticed it before. The person who did my spark plugs suggested it was either 02 censor or catalytic converter. The mechanic that did my exhaust manifold claimed to have replaced my 02 sensor. So if it’s the catalytic converter then it’s a wrap (face palm)
Yeah, the rotten egg smell could be from a cat or O2 sensor that isn’t allowing those gases to be filtered like they should. You should see a check engine light for that if it’s enough to be a problem.
Are the vibrations only at idle, or while you’re driving too? A bad IAC should only affect your idle.
Hi I have a 2003 Mitsubishi eclipse Spyder and I took it to a shop where they told me the code is reading po507 the idle air control valve. I was just wondering if that would cause it to be jerking when it goes into 3rd gear. It is an automatic with the option to use the sport control. Thank you in advance. And have a great day.
It might but I think it’s unlikely.
I have been struggling with my 2005 v6 Ford Explorer Sport Trac … at idle it misfires 3, 2, and 1 … the other side is completely ok. It accelerates fine most of the time but when I give it the gas to quick from a dead stop sometimes it goes into limp mode for a block or so then all of a sudden it run good… still rough idle due to the misfires. I have replaced the plugs, wires, ignition coil 6 pack, had the fuel system cleaned, and replaced the fuel pump. I cleaned the map sensor, and all the sensors I could find and at least one other mechanic cleaned them also. I even tried running premium gas in it. If I am out on the 401 it runs like a champ at 100 km or even 120 km… I feel like a squirrel chasing my tail. 3 mechanics so far have checked for vacuum leaks however found none. I am not made of money and I can’t think of much more to do except maybe the fuel injectors but why would only be on one side of the engine… any more suggestions?
Start with any part you have two of – one for each bank. It might help to take a look at a factory service manual or repair manual to see which parts could cause a whole bank to misfire.
I have a 2008 pontiac G5 and the rpm needle junps up and down when driving usually between 0-50. Any ideas?
This could be an electrical issue with the gauge cluster. Cleaning any electrical contacts related to the tachometer signal may help, or you may have to swap the cluster entirely. A multimeter may help you test to ensure your connections are good.
Some vehicles get their tachometer signal directly from the ignition coils. If an ignition coil has a dirty signal (firing when more often than it should be), it could overheat and fail completely.
Since ignition coils can be spendy, I suggest you check a wiring diagram for your vehicle to see if the tach is driven from the ignition coil (as it is on one of my cars). On these types of systems, there is usually one wire that is a dedicated tach signal. You may have a power, ground, trigger wire, and tach signal. If your tach works this way, then figure out if the ignition coil is the root cause or if the bad connection is limited to the cluster. A repair manual should have this diagram.
If this is all a bit confusing, it might be best to bring it by a shop and describe the issue in as much detail as possible and have them deal with it.
I saw a post where a guys radiator cap was clogged causing the radiator to not be able to pull water from the reservoir. That caused hoses to collapse causing higher load on engine from water pump. Resulting in fluctuating idle when cold. I assume it went away after water heated up to not be trying to pull water from the reservoir. Who would have thought…..
Mine takes bout 10 sec to start! Runs perfect then if sets few hours it does this! I cleans the I A C and M A F
Any ideas 98 Ford v6 c3.8
I’d start with the simple stuff. If your vehicle also cranks slow, I’d have the battery and alternator tested to make sure they are good.
Old thread, but Just had someone bring their truck to me with this problem. To save other people from going down the wrong rabbit hole, it’s not the battery… Once the car is running you can take the battery out completely and it will run just fine in the vast majority of non-ICE/ hybrid automobiles. If the alt is bad then the car will stall out once you pull one of the battery cables when it is running. If either of them are completely shot then the car will not even start after a few days of running once either is completely shot. If you have the idling problem going on for weeks then you are barking up the wrong tree. My first steps would be to do what Dane Brinson said above with the additional steps of checking for vacuum leaks and worn or burnt wiring in the engine bay. The throttle body and sensors have a constant flow of air flowing by them. That will allow buildup of contaminants which will make the sensors not work properly. Try cleaning them first with the proper cleaner (i.e. MAF cleaner for Mass Airflow senor) and if that doesn’t work then get out the multimeter and make sure they test bad before indiscriminately replacing parts. You would be surprised how often just a thorough cleaning will fix the problem.
Hey Jim, thanks for the data point. Appreciate your expertise.
I have 2002 Ford tours an it stalls out sometimes when I turn it off an start it back up it runs rough an want even pull out. After sitting for bout 10 minutes or so it starts up an runs find. Could this b a idle air control valve.
Absolutrly check your throttle body sensors FIRST…far cheaper to replace. A bad throttle body sensor offsets the air/fuel mixture and causes numerous problems, including idle surging. These sensors are IAC (appr. $75), the TPS…throttle position sensor (appr. $30), and MAP sensor …manifold absolute pressure sensor (appr. $30). You can buy an inexpensive obd2 scanner to read you codes… Or Autozone reads them for free.
I have a 5.4 triton has this issue rough idle what should I Ck first
Check for vacuum leaks. This can be done with a smoke test. If you don’t have a smoke tester, you can build your own. Just google “diy smoke tester” and find one that works for you.
If you have no vacuum leaks, it could be the IAC valve. Check the factory manual for diagnostic and replacement procedures.
Could a bad transmission cause your cars rpm needle go crazy when idling I drive a 2002 Cadillac Seville. I don’t have 4000 for a new trans. I,m being told that is the problem. Any ideas welcome
Hi Carol, I would get a second opinion from another mechanic. If your transmission is behaving fine (no jerking, engine speed matches ground speed, etc) you could simply have a bad tach sensor or instrument cluster.
Take off your egr valve, emission gas regulator, if it is clogged up and the cars vacuum cant actuate the diaphragm inside it, it will cause the rough sporadic idle you describe and ultimately effect the transmission, by leading to a clogged catalytic converter, that causes extreme loss in power as the vehicle cant release the exhaust causing back pressure. If you are not racing the transmission not slamming it into park drive reverse i highly doubt it is the transmission. A bad transmission issue would be shift solenoids or maybe cracked torque converter, that would just cause the engine to stall immediately as you put it into reverse or drive if you are in park or neutral and still having idle issues it is not transmission related as the motor is not engaged to the transmission. The egr can be cleaned out with a degreaser and suck on the vacuum port to see if the diaphragm compresses, if it doesn’t or feels like you’re sucking through a straw the diaphragm is bad, replace the egr valve 60-100$ fix if the idle improves but still have lack in power loosen the exhaust at the headers, not muck just enough to allow the exhaust to bypass cats. If driving performance improves you have clogged cats, depending on the car you may have up to 3 example, a v6 or v8 has 2 exhaust headers therefore 2 upstream cats and 1 downstream unless you have dual exhaust then you have 4, 2 upstream and 2 downstream on a 4 cylinder motor has 2, 1 up and 1 down, catalytic converters are not cheap and most often require a muffler shop to install new ones. Simple test take an old rag and cup the tail pipe if it blows your hand off after a few seconds you cats are functioning properly if not odds are one or both are clogged. My bet is on that pesky EGR valve. The only other thing i can think of that would cause a sporadic idle is the Idle Air control valve, this one is activated by electronic solenoid that is governed by your vehicles temperature sending unit these two components work in conjunction with the throttle position sensor ignition timing etc. The IAC can be checked with a volt meter you would have to look up your vehicles operating parameters and use the volt meter to check for abnormal readings, good indication of bad IAC. So in a nut shell you got EGR, IAC, temperature sending unit, not the temp sensor, they are completely different, one shows the temp on your dash the other sends info to the computer why its calls a temp sending unit, because it sends data to the computer.
Hey Carl I had pretty much the same problem and it turned out to be the cluster I replaced my cluster and now everything shifts fine and I was fine have no other problems I did go ahead and replace the IAC but that was just because I wanted to
I had the same car. It was the idle issue. My husband let it go so long that the car eventually would idle so high in drive gas pedal wasn’t even needed. Crazy
I found one for $11 so it pays to search online
Where online did you come across that great deal may I ask?
2004 heep liberty i belive the iac sensor is shot if you do not constantly give it throttle it will stall out. I removed it to see if is sticking but it seems fine. Could the electrical conection been the reaskn for this.
Iac bad wheh car is put into reverse or drive an car wants to die when in park or drive if warmed up doesnt die
Could be the IAC, yes. You may also want to check for vacuum leaks.
I think that you are well today
I am struggling with my honda civic 150i model S03 I think that it’s air control valve as you said ,,, because of it’s up and down idle, overheating then nothing power
1999-2005 Pontiac Grand Am has a screw to adjust idle speed. It is located on bottom side of the throttle body, and easiest to adjust if the throttle body is taken off. Has hex head, tighten to increase idle and loosen to reduce idle speed. I feel turning around 1.25 is good adjustment to test.