Causes of a bad Idle Air Control Valve | Symptoms of a bad IAC Valve

An idle air control actuator or idle air control valve (IAC actuator/valve) is a mechanical unit usually used in fuel-injected automobiles to regulate the speed of the engine when it is idling. Similarly, an idle speed control actuator is used in carbureted vehicles. This article explains the symptoms and causes of a bad idle air control valve and how to fix it.

What is an Idle Air Control Valve?

The IAC actuator sometimes called the IAC (Idle Air Control) valve, is an electrically driven device that receives its input from the engine control unit of the vehicle. It is installed in such a way that it either activates the throttle butterfly valve directly or it can bypass the throttle altogether.

Idle Air Control Valve

The Idle air control valve has a linear servo actuator servomotor. The linear servo actuator servomotors control a plunger that modulates the airflow according to the throttle body’s opening size.  

The engine electronic control unit (ECU) is responsible for digitally controlling both the location of the servomotor and the quantity of airflow. This process makes it possible to maintain a steady idle speed for the engine. The linear servo has a lead screw, a digital optical encoder, and a DC motor.

In order to prevent the engine from stalling, IAC permits the engine control unit to regulate the speed according to the engine load, which is usually known as the anti-stall function. This eliminates the requirement for the driver to push the accelerator simultaneously and start the car by simply releasing the clutch (for manual transmissions) or brake (for automatic transmissions).

Symptoms of a bad Idle Air Control Valve

As the idle air control (IAC) valve goes bad, it gives one of the below-given symptoms:

  1. Irregular idle speed
  2. Check engine light comes on
  3. Engine stalling
  4. Engine backfire
  5. Rough idle
  6. Hesitation under load
  7. Engine won’t start

1) Irregular Idle Speed

Inconsistent idle speed is one of the most common symptoms of a faulty IAC valve. The IAC valve has a preset program that regulates and keeps the engine’s idle speed constant.

Idle speed might be thrown off if the valve fails or develops any troubles. This may lead to an idle speed that is abnormally high or low or, in rare situations, a surging idle speed that continually rises and falls.

2) Illuminating Check Engine Light 

The presence of the Check Engine Light is another sign that there may be a problem with the idle control valve. If the engine control module identifies a problem with the signal or circuit associated with the idle air control valve, it will trigger the Check Engine Light to alert the driver that there is a fault.

The check engine light may start illuminating due to many other faults; therefore, having the computer examined for trouble codes is strongly suggested.

3) Engine Stalling

Engine stalling is another, more severe signal of a bad IAC valve. If the IAC valve breaks entirely, the vehicle may lose its air supply and be unable to maintain a normal idling. This may cause the engine to stall while running, and in certain situations, it can cause the engine to not idle at all and stall as you start your engine. 

4) Engine Backfire

A backfire occurs when flames fly out of your vehicle’s exhaust pipe. The engine backfires when combustion occurs outside of the engine’s combustor. The engine backfiring is also one of the common symptoms of a bad IAC valve. However, your car engine may start backfiring due to some other faults.

In order to determine whether a faulty IAC valve causes the backfires or not, you should accelerate the vehicle. Watch for any jerking as you let your car slow down. Afterward, make sure there are no leaks in the exhaust system.

As your automobile decelerates, pretend it twitches and fuel leaks out your exhaust. There’s probably a problem with the IAC valve.

Read More: Symptoms and causes of Engine Misfire

5)  Rough Idle

Your car’s ability to maintain a steady idle speed may be guaranteed by maintaining a reliable IAC valve. However, your vehicle’s engine will have a rough idle if this valve goes bad for any reason.

Rough idling may cause annoying vibrations whenever you stop the vehicle with the engine running. Idling occurs when your engine doesn’t receive a proper supply of air.  

6) Hesitation Under Load

For instance, if your IAC valve is malfunctioning and you turn on the air conditioner or heater, your engine would likely shut down immediately.

Turning off the car’s heater or air conditioner and other equipment and letting the engine rest for a few minutes may help solve the issue temporarily until you can have it fixed at the repair shop.

7)  Engine Won’t Start

A malfunctioning idle air control valve may change the air-fuel ratio, making it difficult for your engine to start. This symptom is unusual, but it is also the most severe since it is so different from the most typical ones. Your engine won’t start due to many other reasons.

Read More: Causes of bad Engine Control Unit

Replacement Cost of Idle Air Control Valve 

The replacement cost of the idle air control valve varies according to the labor cost and the type of vehicle.

The average replacement cost of the idle air control valve is between $110 and $510. Just the components alone may cost you anywhere from $65 to $410. The labor cost may be from $45 to $100 because removing and replacing the old IAC valve does not take long.

You might save about $90 to 110 by doing this replacement task yourself if you are skilled in vehicle repair.

How to Clean the Idle Air Control Valve

It is necessary to clean your idle air control valve regularly to ensure that it serves you well for as long as feasible. This repair job is not as difficult as it seems at first.

  1. Find the location of the throttle intake manifold. It should have the IAC valve right next to it.
  2. Using a screwdriver, disconnect the air cleaner line.
  3. Simply disconnect the battery wires and unscrew the idle air control valve to remove it.
  4. Make sure your car is turned off fully before you step out of it; otherwise, you might receive an electric shock. Carburetor cleaning should be sprayed on the valve once it has been removed.
  5. To remove the carbon buildup on the valve, take a clean, soft cloth and use it to wash the surface gently.
  6. After you’ve finished cleaning, you may put the valve and wires back where they were.
  7. If your engine’s idle speed still increases unexpectedly after completing this process, the problem is likely with your idle air control valve.

How to Replace a Bad Idle Air Control Valve

  1. Find the throttle intake manifold in your vehicle. Usually, the idle air control valve is located on or near the throttle body immediately next to the intake manifold.
  2. Using a screwdriver, separate the air cleaner line.
  3. Separate the battery connections and unscrew the idle air control valve.
  4. You’ll find an electrical connection on the bottom of your idle air control valve that has to be disconnected. These links can be cut by hand in most cases, but sometimes they get locked and need special tools.
  5. Usually, you’ll need two bolts to fasten your IAC valve in place. Carefully unscrew both bolts and the old IAC valve.
  6. The malfunctioning IAC valve must be replaced with a new one.
  7. Please note that the bolt slot must be aligned while installing the new idle air control valve.
  8. If you disconnected the battery while you were working on the part, you now have to reset the check engine light. Connecting the battery again will get you going immediately.

FAQ Section

What is the function of the Idle Air Control Valve?

A vehicle’s idle air control valve is responsible for adjusting the airflow into the engine when it is idling. In an idling condition, this valve ensures the normal speed of the engine.

What is a Car’s Idle?

The frequency at which your engine operates while your car is not being driven or it is not receiving inputs from the throttle is referred to as the engine’s idle speed. The vehicle’s idle speed is shown on the speedometer gauge in RPM. This speedometer gauge is located on the vehicle dashboard.

Is It Safe to Drive with a Defective Idle Air Control Valve?

Technically, driving with a poor IAC could be possible, but you shouldn’t keep doing this. Stalling is a hazardous driving condition that may be caused by a malfunctioning IAC.

How to clean Idle Air Control Valve without removing it?

  1. Find the vehicle’s idle air valve. It is often located on the throttle body of the engine of a vehicle.
  2. Remove the filter box.
  3. Take out the vent and disconnect the PVC line.
  4. Separate the air intake from the throttle.
  5. Locate the access point for the idle air valve. If you remove the throttle body, you’ll be able to see a little hole; here is where you should concentrate your cleaning efforts.
  6. Use a throttle body cleanser to disinfect the opening. Any car dealership should sell cleaning supplies.
  7. Reconnect all of the parts

How do I know if my idle air control valve is working?

Set your multimeter to “Ohms” mode. A multimeter’s leads are used to check the resistance between two points; one lead is connected to one valve terminal, and the other is connected to the other. A reading of 0.00–0.05 is considered normal. Any deviation from this indicates a faulty idle air control valve.

How do you reset your idle air control valve?

Without a diagnostic instrument, use these steps to reset the IAC valve:

  1. Lightly step on the gas pedal.
  2. Run the engine for 4 to 12 seconds after starting it.
  3. Switch the ignition to “off.”
  4. Wait about 12 seconds.
  5. Start the engine.

Where is the IAC valve located?

Usually, the IAC valve is located on or near the throttle body immediately next to the intake manifold.

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