How to Check an Idle Air Control Valve
The idle air control valve — also known as the "idle speed control valve" — regulates the idle speed of your engine. This is controlled by the engine's computer. Sometimes parts go bad, which results in your car idling strangely or stalling. Check to see if your idle control valve is functioning properly before attempting to replace it.
Identifying Issues with an Idle Control Valve
Look for a high engine idle.A common symptom of a faulty idle control valve can be a high idle. Start the engine and look at the tachometer on the dashboard. Most vehicle’s engines will idle at our below one thousand RPMs. If you are familiar with your engine’s normal idle, compare that to its current RPMs.
- If the vehicle’s engine is idling well above 1,000 RPMs, it’s probably too high.
- Vacuum leaks can also cause a high idle.
Pay attention to low idle or stalling.Aside from high idle issues, low idle and even sporadic stalling can both be attributed to a bad idle control valve. Again, start the engine and compare how it is running at a stop to how it normally runs.
- If the idle is low and inconsistent, it may be due to an issue with your idle control valve.
- Low idles could also be caused by vacuum leaks.
Look for signs of a vacuum leak.If your engine is idling poorly, try to diagnose any possible vacuum leaks that may be causing it. Visually inspect the vacuum lines in your engine bay for signs of damage such as cracks or overly worn areas.
- Remove a vacuum line and connect it to a vacuum gauge to measure the level and consistency of the vacuum.
- You can also try spraying a soap and water mixture on the lines to look for bubbling at the point of a leak.
Take note if the check engine light comes on.The check engine light in your vehicle is designed to turn on if the Engine Control Unit (ECU) identifies an issues with how the engine is running. Look at your dashboard; if the check engine light is on in conjunction with idle issues, it may be because the idle control valve is malfunctioning.
- The check engine light looks like a simple drawing of an engine.
- A check engine light in conjunction with idle issues can be indicative of a faulty idle control valve.
Method 1 Quiz
Your engine may be idling too high if it idles above what RPM?
Checking to See if the Idle Control Valve is Functioning
Use a code scanner to check error codes.If your vehicle was built prior to 1996, you will need an OBD I scanner. Vehicles made after 1996 will need an OBD II scanner. Connect the code scanner to the port beneath the dashboard and turn it on. Once connected, use the scanner to bring up the error codes making the check engine light come on.
- In some code scanners, it will provide the English description of the error code on the read out.
- If your code scanner does not, you will need to look up the code the scanner shows you to find out what it is.
Start the engine and take note of the idle RPMs.Insert the key into the ignition and start the engine. Wait a minute for the engine idle to level off, then use a pen and paper to write down the RPMs that your engine settles and idles at.
- You may need to let the engine run for a few minutes in order for it to come down to its normal idle speed.
- Keep the paper you write the RPMs on handy so you can compare it to the engine’s idle as you continue the test.
Shut the car off and disconnect the Idle Control Motor.With the idle RPMs noted, shut the vehicle back off and remove the key from the ignition. Open the hood and locate the Idle Control Motor. Once you locate it, disconnect it.
- The way to disconnect your Idle Control Motor will vary from application to application; refer to your vehicle’s service manual for more specific instruction as to how to disconnect it.
- You can usually disconnect the idle control motor by unplugging the wiring clip going into it.
Restart the engine.With the Idle Control Motor disconnected, get back into the vehicle and start the engine again. The engine should still start and run without any issue despite the idle control motor being disconnected.
- Be sure to tuck the wiring you disconnected up in the engine bay so it doesn’t get caught in any moving parts.
Look for a difference in idle speed.Allow the engine to run for a minute so it settles to a consistent idle, then take note of any difference in the idle RPMs versus the idle you observed earlier. If the idle has not changed at all, it’s likely because your idle control motor has not been functioning.
- If the idle control motor was working, disconnecting it should have created a difference in the engine’s idle.
- This test confirms there’s an issue with the idle control motor, but not what the issue may be.
Shut off the engine and reconnect the Idle Control Motor.If you identified a difference in engine idle RPMs with the Idle control motor connected and disconnected, confirm your hypothesis by reconnecting it and starting the engine again.
- The idle should go back to what it was when the idle control motor was last connected.
- Refer to the note you took about idle RPMs to compare it to your first reading.
Method 2 Quiz
If your idle control valve were functioning correctly, disconnecting it and idling the car would cause:
Checking for Issues in Specific Makes
Use a test light to check the wiring on a GM idle control motor.Take a test light and connect the negative lead to the body of the vehicle. Press the test light into each of the four circuits on the GM idle control motor. Each circuit should make the test light flash or go from bright to dim while the engine is running.
- If the test light doesn’t flash on each circuit, the issue is coming from the ECU, not the idle control motor.
- If the test light flashes properly, it means the idle control motor needs to be replaced.
Measure the resistance of the solenoid in a Ford.Locate the idle control motor in your Ford vehicle and identify the two electrical pins on the solenoid. Connect an Ohm meter to the two and measure the resistance between them.
- Fords are designed to operate with the resistance in the solenoid in a range between 7.0 to 13.0 ohms.
- If the resistance is outside that range, the idle control motor needs to be replaced.
Use a bidirectional scan tool to increase idle speed in a Chrysler.Connect a bidirectional scan tool to the same OBD port you would plug a code scanner into. Use the command in the scan tool to increase the engine’s idle. If the engine idle does not increase, it means there is an issue at the idle control motor of its circuit preventing the signal from changing the idle.
- You can purchase a bidirectional scan tool at your local auto parts store.
- Make sure the wiring harness is firmly connected to the idle control motor before conducting this test.
Method 3 Quiz
When using a test light to check the wiring on a GM idle control motor, what does it mean if the test light flashes properly?
QuestionWhen I slow down or when I stop at a red light my car dies. Could this be due to the idle air control valve?wikiHow ContributorCommunity AnswerIt's possible. A faulty idle control valve can leave the engine idling at too low an RPM for it to continue running.Thanks!
QuestionThe engine only runs when my foot is on the gas pedal. What's the deal?wikiHow ContributorCommunity AnswerIt's possible that a faulty idle control valve can leave the engine idling at too low an RPM for it to continue running.Thanks!
QuestionWhat would cause my car that idles fine not to idle down when coming to a stop? The IAC has been replaced.wikiHow ContributorCommunity AnswerIf replacing the ICV or IACV and problems still persist, test all the vacuum hose lines as mentioned in the steps above using soapy water.Thanks!
QuestionWould bad ICV make the car hard to start after it has run for a time?wikiHow ContributorCommunity AnswerNo. The idle control valve should have very little to do with how the vehicle starts.Thanks!
QuestionWhat could the problem with my car be when it wants to idle way too slowly?Nick FlorenceCommunity AnswerIf 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.Thanks!
QuestionI 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?wikiHow ContributorCommunity AnswerFix 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.Thanks!
QuestionIs an idle control valve the same thing as an idle control motor?wikiHow ContributorCommunity AnswerThe idle control valve sits atop the idle control motor. They are two separate though coordinating entities that function to regulate your car's idle speed.Thanks!
QuestionIs there any risk using car with idle control problems?wikiHow ContributorCommunity AnswerNot 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.Thanks!
QuestionCan a bad idle air control valve cause the RPM to idle a little high and come down slowly to normal rpm range?wikiHow ContributorCommunity AnswerNormally, 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.Thanks!
QuestionCould a bad IAC valve cause a car to lose power when the motor has been running for a bit?wikiHow ContributorCommunity AnswerYes, that can happen.Thanks!
When I start my car and turn on my a/c my rpm go op and down?
If my car engine cuts off when I turn on the A/C, could it be a problem with the idle air control valve?
Replaced IAC valve, started car and now the RPMs are between 6-8 without touching gas pedal- on 2002 Malibu 3.0 L V6?
I replaced the IAC valve and started the car,. Now the Rams are between 6-8 without touching the gas pedal. This is on my 2002 Malibu 3.0 L V6. What should I do?
What can cause an "Idle Switch, open circuit since ignition on"?
Sources and Citations
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Video: How To Test and Replace Idle Air Control Valve P0505 HD
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