Idle Air Control Valve (IAC Valve) – Everything You Need To know

An idle air control valve (also known as the IAC valve) is a device that is used in fuel-injected vehicles to control the engine’s idling rotational speed.

The idle air control valve lets the engine idle smoothly than stalling out when the vehicle is stopped.

This article will focus on the IAC Valve (Idle Air Control Valve) in the engine. After reading this article, you’ll be able to understand the basics of the IAC valve, symptoms of a bad IAC valve, average replacement cost, and cleaning tips.

Let’s get started!

The engine will continue to idle until you press the accelerator. As soon as the car’s accelerator is pressed, the vehicle is then set into motion again.

The engine speed of a gasoline engine relies upon the idle air control valve (IAC valve). When you press the gas pedal, the throttle plates open and permit airflow into the intake manifold. A higher throttle will result in more airflow and a faster engine.

When the main throttle section gets closed, and the accelerator pedal is relaxed, the airflow decreases, and the engine speed decreases. 

If there is no airflow, the engine will not run at its maximum speed. This can be dangerous if you are waiting for your vehicle to move again when you are on the road. The idle air control valve (IAC valve) bypasses the closed throttle plates and helps prevent the engine from stalling. 

Based on its design, the IAC valve can be detached, attached, or removed and included as part of the main throttle body.

Why Are IAC Valves Important?

One might wonder, “Why is the idle air control valve so complicated?” wouldn’t it be better to bypass the IAC valve? Wouldn’t it be better to hold the throttle plates slightly open?

This did work in carbureted engines, but they were not particularly responsive or efficient. An engine with fuel injection may lose performance and cease to function if its throttle case is fixed due to air conditioning and power steering loads. This situation requires variable idle control.

Computer sensors and electric fuel injection make it comfortable to efficiently have a responsive idle control. The bypass is usually regulated by an automatic or electronic IAC valve, depending on how stressed the engine is at that moment. The idle air control valve may open delicately if the engine is under no pressure or stress. 

Parking maneuvers can cause power steering and electrical loads to slow the engine. However, the IAC valve, which uses feedback from the engine speed sensor, opens slightly more to maintain consistent engine speed and sufficient power to avoid stalling.

It is important to remember that in older cars, the throttle actuator is used instead of the IAC valve since it can serve the same purpose.

Also Read: Neutral Safety Switch (Everything You Should Know)

Idle Air Control Valve Symptoms

IAC valve

Have you ever wondered what happens when an IAC valve malfunctions? If the IAC valve fails, it causes different problems in the vehicle. 

Below are a few symptoms of a bad IAC valve.

1. Incorrect Idle Speed

The car will feel like it’s going to stop as your RPMs drop. An IAC valve that is left open will cause an excessive idle speed. Even though the engine is not running, it will still run very fast.

Bad IAC valves can cause surging conditions at idle. The RPMs will rise and then drop to normal.

2. Check Engine Light Is On

The automatic car sensor oversees the IAC valve to ensure its adequate function. The sensor triggers the check engine light if it detects a fault. 

3. Car Stalling

A bad IAC valve can cause a vehicle’s engine not to get enough airflow to move, causing it to stop completely. 

4. The Car Won’t Start

In extreme cases, the IAC valve may prevent air from entering the engine when it is functioning, resulting in an engine that won’t start or crank. 

How To Test Idle Air Control Valve

You can test the idle air control valve with a Multimeter to see if it is faulty. A functioning IAC valve on the Multimeter shows that the valve is clean.

On the other hand, it should be replaced if the test doesn’t show a functioning valve.

Tools and accessories such as a socket wrench, Multimeter, an electronic parts cleaner, screwdriver, and a 10mm socket are used to conduct the test. 

Here is how to test your IAC valve With a Multimeter:

  1. Open the hood. Rotate the ignition key to the left side and remove the idle air control valve.
  2. Pull the plug from the control valve. Pull the release tab from the top.
  3. Remove the idle control valve, and spin it over. The valve openings should be visible.
  4. Set your multimeter to “Ohms”.
  5. One multimeter lead should be touched to one end of the valve terminal, and the other should do the opposite. Normal readings are between 0.00 to 0.05. Any reading above this level indicates that your idle air control valve may be defective.
  6. If your valve reads normal, check the valve openings to see if any dirt is present. If the valve is functional, you should be able to see dirt on its sensor.

How To Replace Idle Air Control Valve

How To Replace Idle Air Control Valve

Replacing an IAC valve is an easy task. follow these steps to know how to replace an IAC valve!

1. Disconnect The Battery

Once the vehicle has cooled in a safe place, remove the battery cable and the negative battery cable and put them aside.

2. Locate The IAC Valve

The make and model of the car will determine the location of the idle control valve. The precise spot will be provided in your vehicle’s manual. Nearly always, the valve is located on an intake manifold.

3. Disconnect The Wiring Harness

Locate the wiring harness that is connected to the IAC valve, and then disconnect the electrical terminal.

You will find a clip or tab that needs to be removed. It might be easier to remove it gently with a pair of pliers.

4. Disconnect The Old Idle Control Valve

Each retaining bolt of the IAC valve should be removed. The valve should now pull out of its place after the wires and bolts have been removed.

5. Clean The IAC Valve Seat

The valve seat should be exposed. Use the throttle body cleaner for cleaning the area where the new valve will be attached. This will ensure a tight seal between the seat and valve.

6. Install The New Valve

Compare the old valve with the new one. Verify that all wiring connections, retaining bolt pattern, and seat placement are the same.

Install the valve and retaining bolts. You can tighten them one at a time using your socket and ratchet.

Note: Do not tighten the bolts too much as it could cause leakage or other problems with the system.

7. Reinstall The Wiring Harness

Attach the wiring harness to your valve. In order to guarantee a secure connection, make sure the terminal makes a good connection.

8. Reconnect The Battery

Attach the negative cable from the battery to it. To prevent engine vibrations from robbing the bolt, tighten it. This will bring back the engine’s power.

9. Test The Vehicle Idle Speed

Start the engine and watch the idle speed. Your vehicle’s specific characteristics and the ambient temperature will determine the idle speed.

It should be between 550 RPMs when the outside temperature is high and 1,000 RPMs at cooler temperatures.

A properly functioning idle control valve can make a big difference in your vehicle’s driveability. This valve can be replaced by anyone, even beginners.

You could economize and save up to $100 if you do the valve installation yourself.

You only need a little confidence and a guide in carrying out the job, or you can pay a professional to get the valve fixed.

Expenses made on replacing the IAC valve are usually low. Lack of maintenance and replacement of the control valve could cause damage to the engine, resulting in a very high cost of repair.

Also Read: Valve Cover Gasket Replacement (Everything You Should Know)

Frequently Asked Questions

What is an idle air control valve?

An idle air control valve (also known as the IAC valve) is a device that is used in fuel-injected vehicles to control the engine’s idling rotational speed. The idle air control valve lets the engine idle smoother than stalling out when the vehicle is stopped.

How do I know if my idle valve is bad?

You will notice fluctuations in RPM and even engine stalling if the idle air control valve is bad. You will also see a layer of carbon buildup in the valve when you inspect it.

How do I reset my idle air control valve?

To resent the idle air control valve slightly Depress the accelerator pedal and turn on the engine. Let it run for 5 seconds then turn it off for 10 seconds. Start the engine again and then check that the vehicle is idling properly

What does the idle air control valve do?

The idle air control valve controls how much air is allowed to enter the throttle. This allows you to adjust the RPM to suit your needs.

How do you check an IAC-valve?

Although the IAC valve is under your car’s hood, its exact location will depend on your car’s make/model. It is mostly situated on the throttle body and connected to a sensor via multiple wires.

How do you clean an IAC valve?

Once you have moved the IAC valve, remove it from the screwdriver and disconnect all wires. It can be cleaned by placing it in gasoline and then blowing compressed air into the valve. Next, attach it again with screws and connect the wires.

Can a bad IAC cause overheating?

In most cases, an inefficient IAC valve won’t cause excessive heating. Many cars have electric cooling fans, which can be turned on whenever the ignition is switched.

Conclusion

An idle air control valve (also known as the IAC valve) is a device that is used in fuel-injected vehicles to control the engine’s idling rotational speed.

The idle air control valve lets the engine idle smoother than stalling out when the vehicle is stopped.

A car may be functioning and not stalling, yet the valve still needs cleaning.

If the car pedal is not sticking or the vehicle isn’t slowing, the valve and body should be cleaned and possibly replaced.

Throttle system maintenance should be a regular habit by cleaning, replacing, or repairing the parts as needed. Ensure that you replace and repair any damaged parts as soon as possible. 

A lack of maintenance may result in other parts being damaged or the malfunctioning of the valves, causing stalling, which is unsafe and stressful.

Scott Greene is a seasoned automotive technician for over 5 years and has been deep into advanced automotive diagnostics for a couple of years. He Loves writing about Automotive Diagnostics and Repair, Trouble codes, Buyer guides for various car parts and accessories, and lots more. 

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