Top Symptoms of Bad Idle Air Control Valve & Replacement Cost

An idle air control actuator or idle air control valve (IAC 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 replace the IAC valve.

What is an Idle Air Control Valve?

The idle air control valve (or IAC valve) is an electrically driven device that is responsible for regulating the engine’s idle speed. It receives its input from the powertrain control module (PCM) of your vehicle.

It is installed in such a way that it either activates the throttle butterfly valve directly or 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 PCM 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 backfires
  5. Rough idle
  6. Hesitation under load
  7. The 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.

Unstable Idle Speed

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) Check Engine Light Illumination

The illumination of the Check Engine Light is one of the clear signs of a bad idle control valve. When the PCM of your vehicle 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.

check engine light

The Check Engine Light may also be caused by a number of faults; therefore, having the computer examined for trouble codes is strongly suggested.

Read More: Causes of Check Engine Light Illumination

3) Engine Stalling

Engine Stalling, Symptoms of a bad Idle Air Control Valve

Engine stalling is another, more severe signal of a bad idle air control 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.  

Read More: How to prevent an engine from stalling?

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.

backfire due to a faulty Idle Air Control Valve

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.

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 Idle, signs of bad IAC valve

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.  

Read More: Why Car Shakes at Idle?

6) Hesitation Under Load

For instance, if your IAC valve is malfunctioning and you turn on the air conditioner or heater, your engine will 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

Car not starting

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: 13 Reasons Why a Car Won’t Start?

Causes of Bad IAC Valve

An IAC valve goes bad due to one or more of the following causes:

  • Carbon Accumulation
  • Damaged Electrical Connections
  • Mechanical Failure
  • Vacuum Leaks
  • Poor Maintenance
  • Faulty PCM/ECM
1) Carbon Accumulation

Carbon may accumulate on your vehicle’s idle air control valve with time. This accumulated carbon may badly affect the performance of the valve and reduce its ability to control airflow. This accumulated carbon may produce due to a combination of oil vapor, dirt, and fuel residues.

2) Damaged Electrical Connections

The valve depends on the electrical connections and wiring to properly collect signals from the powertrain control module (PCM) and alter the idle speed accordingly.

Damaged or loose electrical connections may disturb the message between the PCM and the IAC valve, causing poor functioning.

3) Mechanical Failure

The IAC valve of your vehicle contains different rotating parts, including a plunger or pintle that regulates the airflow. Over time, these parts may be damaged, become stuck, or worn out, stopping the valve from working efficiently.

4) Vacuum Leaks

A vacuum leak is one of the major causes of a bad idle air control valve. Your IAC valve works along with the intake manifold vacuum.

A leak in the vacuum system, like damaged gaskets or hoses, may disturb the vacuum pressure and lead to the poor performance of the IAC valve.

5) Poor Maintenance

Poor-quality fuel or poor maintenance of the engine may cause an accumulation of dirt in the throttle body, intake manifold, or IAC valve. These contaminants may create problems in the smooth motion of the IAC valve or block the air channels, disturbing idle control.

6) Faulty PCM/ECM

In some cases, a malfunctioning PCM may send the wrong information to the IAC valve. When the valve receives wrong information, it may perform erratically or not respond properly according to the conditions.

Read More: Bad PCM Symptoms and Causes

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.

  • Find the location of the throttle intake manifold. It should have the IAC valve right next to it.
  • Using a screwdriver, disconnect the air cleaner line.
  • Simply disconnect the battery wires and unscrew the idle air control valve to remove it.
  • 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.
  • To remove the carbon buildup on the valve, take a clean, soft cloth and use it to wash the surface gently.
  • After you’ve finished cleaning, you may put the valve and wires back where they were.
  • 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 IAC Valve

  • 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.
  • Use a screwdriver and remove the air cleaner line.
  • Remove the battery connections and unscrew the idle air control valve.
  • 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.
  • Usually, you’ll need two bolts to fasten your IAC valve in place. Carefully unscrew both bolts and the old IAC valve.
  • The malfunctioning IAC valve must be replaced with a new one.
  • Please note that the bolt slot must be aligned while installing the new idle air control valve.
  • 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 bad 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 valve.

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?

  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?

The idle air control valve is usually located on or near the throttle body immediately next to the intake manifold.

What are the signs of a bad IAC Valve?

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

Can a bad idle air control valve cause hard starting?

Yes, a bad idle control valve may cause hard starting. When this valve becomes faulty, it restricts the proper flow of air to the engine. An insufficient flow of air to the engine may lead to a hard engine starting.

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