Q&A for How to Check an Idle Air Control Valve

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How do I know if my vehicle has a problem with the idle air control valve?

Hovig Manouchekian
Auto Repair & Design Specialist
Hovig Manouchekian is an Auto Repair and Design Specialist and the Manager of Funk Brothers Auto, a family-owned business operated since 1925. With over 30 years of experience in the automotive industry, Hovig specializes in the process of auto repair and maintenance. He is also very knowledgeable in common automotive issues and needs including engine repair, battery replacement, and windshield accessory and maintenance. Hovig's knowledge and hard work have contributed to Funk Brothers Auto winning Angie's List Super Service Award for five consecutive years.

Hovig Manouchekian

Auto Repair & Design Specialist

Expert Answer

If your check engine light is on, that may help with the diagnosis. Also, if you have a modern vehicle with an OBD2 system, you can check your idle air through scan tools. On older vehicles, try to check the resistance that's going to the valve from the vehicle. You can also try to manually activate it to see how the car reacts—you may be able to isolate the problem to the valve.

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Question

When I slow down or when I stop at a red light my car dies. Could this be due to the idle air control valve?

Community Answer

It's possible. A faulty idle control valve can leave the engine idling at too low an RPM for it to continue running.

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Question

The engine only runs when my foot is on the gas pedal. What's the deal?

Community Answer

It's possible that a faulty idle control valve can leave the engine idling at too low an RPM for it to continue running.

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Question

What would cause my car that idles fine not to idle down when coming to a stop? The IAC has been replaced.

Community Answer

If replacing the ICV or IACV and problems still persist, test all the vacuum hose lines as mentioned in the steps above using soapy water.

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Question

Would bad ICV make the car hard to start after it has run for a time?

Community Answer

No. The idle control valve should have very little to do with how the vehicle starts.

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Question

What could the problem with my car be when it wants to idle way too slowly?

Nick Florence

Community Answer

If your idle is too low, it could be the IAC not talking to the computer correctly. Disconnect the IAC connector for a couple seconds while your engine is idling. If your engine idle didn't change, you can suspect it to be the IAC. If it is working properly, unplugging it would cause your idle to freak out. Also check the wires going to the IAC connector.

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Question

Can a bad idle air control valve cause the RPM to idle a little high and come down slowly to normal rpm range?

Community Answer

Normally, if you just start your car, the idle air control valve will cause the engine rpms to increase and slowly decrease. That would be a sign that your IAC is working.

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Question

I have 98 Dodge Caravan Sport with a 3.3 V6. It has a rough idle at start, the check engine light is on, and the idle corrects itself usually after 20 to 30 seconds. I can also correct the problem by disconnecting a vacuum line for a few seconds. What could be wrong with my engine?

Community Answer

Fix the Check Engine Light first, You can get a reader for free at autoparts store. Once you know what the code says, you can start figuring out solutions.

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Question

Is there any risk using car with idle control problems?

Community Answer

Not usually. The idle control valve only effects the engine while your foot is not on the gas. As long as the vehicle isn't idling at too high an RPM or stalling, it should function with a faulty idle control valve.

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Question

How do I understand car error codes?

Community Answer

Google the code along with the make of your vehicle, i.e. "Toyota P0505" for OBDII or "Ford 214" for OBDII.

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Question

Where on the motor is the idle control valve located?

Community Answer

It's located to the right of the throttle body on my 2003 Durango. I had to use a full-version Chrysler shop manual to find it the first time.

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Question

Could a bad IAC valve cause a car to lose power when the motor has been running for a bit?

Community Answer

Yes, that can happen.

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Question

When I start my car and turn on my A/C, my rpm goes up and down. Why?

Community Answer

They go up because of the engine load from the A/C being on dragging on the pulley. It is best to turn on A/C at speeds higher than 25 mph.

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Question

My car buckles when I accelerate around 20 mph, then loses power and shuts off. It starts back up fine but revs high. Why might this be happening?

Community Answer

It's probably a clogged air filter or faulty/dirty MAF sensor. Your symptoms indicate starvation for air or fuel, most likely air. When a vehicle loses power and shuts off, it's typically the MAF.

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Question

Should my vehicle stall after restarting when unhooking the idle air control valve?

Community Answer

No, just the RPM should go down (where 'unhooking' means electrical disconnect).

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Question

Could the idle control valve cause my car to rev up a bit in between gear changes?

Community Answer

That's normal for every car.

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Question

Are smog tests affected in any way if the air control is not good?

Community Answer

Absolutely. If airflow is restricted/limited, your air-fuel mixture will not be in proper alignment, likely resulting in a failed emissions test.

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Question

Is a high idle on my vehicle a sign of a bad air control valve?

Community Answer

It could be but depending on the vehicle it could also be, among other things, a vacuum leak or an air pocket in the cooling system if it uses a temperature controlled fast idle valve separate from the IAC .

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Question

Is the idle air control the same as the RPM sensor?

Community Answer

No. The RPM sensor represents an input to the ECU, telling it what the RPM is. The IAC takes the output from the ECU to actually set the RPM to the correct value. The two work together with the ECU to form a closed control loop.

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Question

Can the idle control valve be cleaned and operate properly?

Marcelino De Sousa

Community Answer

Yes, you can clean it but after you clean it and the body throttle with carburetor cleaner, it should fix the problem. An idle/air control valve can be tested if you let the engine run for a few minutes, then switch off the engine, disconnect the plug on the I/ACV and start. If you see the revs have dropped, then it is not the unit, it is something else.

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Question

What is causing a high start up of high RPM in my vehicle?

Community Answer

Remove the throttle body and spray the insides with a carburetor spray cleaner. Spray the orifices and all around the throttle plate. Don't be afraid to spray a lot. Get all of that black soot out. Use an air compressor to dry out the throttle body after spraying. Let it dry out, then re-install the throttle body, and start the car. After doing this, it should be a lot better than it was.

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