How to Change an IAC Valve on Your Car Without A Mechanic
You’re heading to the store one day and your car stalls unexpectedly in the intersection. You’ve never had any issues with it before, so it worries you a little. When you finally get to the store, you sit in the parking lot with the car running to pull together your things before you head inside. As your car idling, you begin to notice that it’s idling at irregular speeds. Now, you’re sure you’ve got a problem. It’s likely that the IAC valve is what’s causing the issue.
What is an IAC Valve?
An IAC Valve is also known as the idle air control valve, and it’s responsible for regulating the way your car idles when it’s not in drive. When your car is idling, or not in drive with no pressure being applied to the accelerator, the computer in your car must maintain a minimum of RPMs so that the engine will remain on and ready to go when you’re ready to drive. If those RPMs aren’t maintained, then your car will stall out or idle roughly. The IAC valve is what maintains those RPMs while you’re idling.
The IAC valve is electronically controlled by the vehicle’s engine control unit. It is fitted so that it either bypasses the throttle or controls the throttle butterfly valve directly. The valve, or actuator, is made up of a servo actuator servomotor and so the amount of air bypass is controlled directly by the engine control unit.
If the idle air control valve fails, then your car can stall out, idly roughly, or cause a sudden increase and decrease in RPMs while you’re at a stop. The check engine light may also come on.
How Long Does It Last?
The IAC valve is supposed to last for the lifetime of the vehicle, but sometimes it does fail or malfunction. This can happen for a number of reasons; the most common being that dust, dirt, or sometimes oil partially or completely jams the actuator and does not allow it to be smoothly controlled.
Over the years that you drive your vehicle, the engine parts can build up quite a bit of carbon as the car runs. The more carbon that builds up in the engine bay, the harder it will be for the idle air control valve to have the right amount of air pass through it.
Is It An Engine Vacuum Leak?
If your engine speed is too high or stalling, then you might have an engine vacuum leak instead of an issue with the IAC valve. When you check the IAC valve and you see it extended all the way, then the engine has an air leak and the computer is trying to compensate for that by changing the idle speed.
Is Your Vehicle a “Drive-By-Wire” Vehicle?
If you have a newer model vehicle, you may have a drive-by-wire induction system that uses an angle sensor on the accelerator to calculate the throttle input. This means that your vehicle likely doesn’t have an IAC valve because the computer gets its information from the sensors and automatically adjusts the idle speed. If it’s malfunctioning, then you’ll likely need to use a professional scanner to reset the system.
Checking the IAC Valve
To check whether your IAC valve is failing, first disconnect the negative battery cable from your battery. Then unplug the IAC connector. Once you’ve done that, you can test a few different things to see if your IAC valve is failing.
Testing the Coil Driver Circuits in the IAC Valve
Measure the resistance between pins 3 and 2 on the valve using an ohmmeter. If the valve is working correctly, then the resistance should ready between 10 and 14 ohms. If it’s not the correct, then you’ll need to replace the valve.
If it is, measure the resistance between pins 1 and 2. Again, the resistance should measure between 10 and 14 ohms. If it’s not, then you need to replace the valve.
Testing the Voltage Lead
Using the voltmeter, check the voltage at terminal 2. Measure the voltage between terminal 2 and ground with the ignition turned to On. The voltage should be battery voltage, and if it isn’t then the circuit needs to be replaced. If it is, test the signal return.
Testing the Signal Return
Double check the voltage at terminal 1 with the ignition turned to On. When you check the voltage between terminal 1 and ground, it should read between 6.0 and 8.5v. If it’s not, then you need to replace the circuit. If it is, move on and try checking the ground circuit.
Testing the Ground Circuit
Pick up the ohmmeter again and check the resistance at terminal 3. When you turn the ignition to On, measure the resistance between terminal three and ground. It should be at 0 ohms. If it’s not at 0 ohms, then you’ll need to replace the valve.
How Much Does a New IAC Valve Cost?
It depends on the make and model of your vehicle. Because the valve is controlled by the computer system, more sophisticated engine control computer systems will require a more expensive valve. For example, you can expect an idle air control valve to cost close to $1000 for a newer model BMW. Less sophisticated computers, therefore, will require less expensive IAC valves. For an older model, mid-sized sedan, you can expect the part to cost anywhere from $100-300.
It’s unnecessary to have a mechanic replace the valve, since it’s usually easily reachable inside the engine bay and doesn’t require too many tools or much time to replace. If you’re up to the task, then you can save yourself the labor costs and do it yourself.
Replacing Your IAC Valve
To replace your IAC valve, here are the materials you will need: A cleaner for the throttle a pair of pliers, your replacement idle control valve, and a socket set and ratchet.
First, disconnect the battery by disconnecting the negative battery cable from the battery and setting it off to one side. Next, locate the valve. Check your vehicle owner’s manual to find the exact location of the valve, but you can usually find it on the intake manifold of your vehicle.
Find the wiring harness that is connected to the valve and pull the electrical terminal from the valve. You’ll have to remove it by disconnecting a clip or a tab so it might be useful to use the pliers to remove it.
Once you’ve removed the wiring harness, you can remove the old idle control valve. Make sure to remove each of the valve’s retaining bolts. Once those are removed, you should be able to just pull the old valve out. After pulling the valve out, carefully clean the area that you’ll attach the new valve to with the throttle cleaner.
Compare the old and new valve to make sure that the two have identical wiring terminals, retaining bolt pattern, and seat placement. If they don’t match, you’ll need to get a different valve that is the same at the old one. You can avoid this mixup by taking the old valve with you to the store when you go to buy the new one.
Put the new valve into place and re-install the retaining bolts. Make sure that you don’t over-tighten the bolts so you can avoid a leak or malfunctioning system. Once the valve is secured into place, reconnect the wiring harness to the valve. Make sure the connection is secure so the engine doesn’t vibrate the harness loose.
Reconnect the battery and start the engine. To test it properly, let the engine idle for 15 second and then turn the ignition back to the OFF position. Wait 15 seconds, and then restart the engine. Let it idle for a little bit and make sure that the RPMs are holding steady at the recommended level for your vehicle. Usually you want the car to idle around 1000 RPMs.
A Working IAC Valve Makes a World of Difference
When the idle air control valve is working properly, then you won’t have to worry about your vehicle stalling at odd times or the car idling weirdly. Replacing the valve is easy and can be done by beginners. If you’re worried that you might not replace it correctly, you can always call a mechanic. If you do it yourself, you’ll save yourself a bit of money and learn more about how to take care of your vehicle.