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What are the Common Idle Air Control Valve Signs?

Idle Air Control Valve Signs

The car’s idle air control valve is found on the fuel-injected engine’s throttle body. It works together with the engine control unit or ECU to control the airflow to the engine. This can help ensure that the car idles smoothly and does not stall when it is stopped, like when you are stopping at a stop sign. It will keep on doing its task until it is time to move the car again. But this car component is not without fault. Over time, it can fail because of carbon build ups or faulty valve-related parts. If it is failing, you may experience some bad idle air control valve symptoms such as unstable RPMs when the car is idling, an illuminating check engine light, engine idling roughly, car stalling, and exhaust backfiring. 

Auto Repairs Are EXPENSIVE


What is the Function of the Idle Air Control Valve?


One of the main components that is controlled by the engine control unit or ECU is the idle air control valve. With it working with the ECU, it controls the idle speed of the engine by regulating the amount of air flowing around the closed throttle plate. It controls the  engine’s idle speed by bypassing air around the throttle plate through a built-in conduit on the throttle body


The throttle is completely closed whenever the engine is idling. To keep the engine running, it will only need a small amount of air and this air will be provided into the engine through the idle air control valve. This can be done since the idle air control valve has a valve-opening coil or a solenoid that opens and closes to control airflow. The amount of air supplied is controlled and determined by the ECU. You can trust that the needed amount of air can be maintained and will be adjusted to respond to the changes in the engine load since it is electronically controlled. 


Electronically controlled means that the valve is electrically operated. One example of this is the stepper motor type of idle air control design. This type of idle air control has a tapered pintle that has 125 different positions. It starts with position zero that translates to a fully extended position or air bypass closed while position 125 translates to a fully retracted pintle which means the air bypass is a hundred percent open. 


The higher the position, the higher the idle speed RPM is. Higher air bypass leads to a higher idle speed for starting, deceleration or accessory loading. So when there is less air circulating, the idle speed will also be slower. 


The engine control unit can control the idle air control valve by providing battery voltage to either of its two internal motor windings. One of the said windings works by extending the pintle while the other one retracts it. The ECU needs to actively control the idle speed, adjusting it all the time to supply what the engine needs depending on its condition or load. For instance, when the air conditioner compressor is turned on, the engine control unit responds to it by opening the air bypass to keep the RPM from dropping.


The idle air control valve is an important component of the car. It makes sure that the car idles smoothly until the car starts to run again from a stop. However, as important this part is, it is not built to last forever. It can become faulty over time. When this happens, you might encounter some bad idle air control valve symptoms. 


Idle Air Control Valve Symptoms: How Do I Know If My Idle Air Control Valve is Bad? 


Knowing the bad idle air control valve symptoms can help you determine if the issues your car is experiencing are caused by a faulty IAC valve. The common bad idle air control valve symptoms include:

  • RPMs are not stable when the car is idling.


One of the most common bad idle air control valve symptoms is an unstable RPMs when the car is idling. It is already given that when the idle air control valve is faulty, the car will not idle properly. You may notice this problem when you’re idling and you see your engine speed fluctuating up and down. 


You may also be able to hear the engine speeding up and slowing down in the 100 to 200 RPM range. This can happen for no reason at all, even if you did not touch any controls of the car. It can be a hassle when issues like this occur since fluctuating idle speeds can cause performance problems in your engine. It is recommended that when you experience this common idle air control valve symptom, you should have it checked and repaired as soon as possible. 


  • The check engine light is turned on. 


The check engine light comes on to alert the driver that there is something wrong with your car. Although there are a number of reasons that can trigger the check engine light to illuminate, a faulty idle air control valve is one of them. This is because the idle air control valve plays a crucial role and can affect the overall performance of the car. The ECU can set off the check engine light if irregular RPMS while the car is idling is detected. An illuminating check engine light, plus any of the bad idle air control valve symptoms can indicate that there is really something wrong with your IAC valve. 

  • Car is stalling.


Car stalling can also be caused by a number of issues, but a bad idle air control valve can be one of them, especially if the car suddenly stalls for no reason at all. This can happen because of two reasons – the ECU can’t maintain the engine speed and the idle air control valve has failed.


When the idle air control valve becomes faulty, the engine control unit will have to control and maintain the engine speed by itself. The ECU might not be able to manage the task by itself. The issue will get worse eventually and with the ECU failing to maintain the engine speed, allowing the RPMs to keep on dropping. The engine will stall when the RPMs become too low. 


The reason why the engine can stall when the idle air control valve has failed is that it can cause the engine to not get enough air while at idle. If the engine is struggling to get enough air, the combustion process will not go through which can lead to engine stalling.

  • Engine not idling smoothly.


An engine that is not idling smoothly is also one of the most common bad idle air control valve symptoms. The idling can become rough when the ECU is no longer capable of adjusting the engine speed since the damaged idle air control valve is throwing it off.  


A properly working idle air control valve should always be giving a smooth idle. The idling should always be smooth even when you are just starting up or when stopping at a red light. You will be able to tell if it is rough idling when you feel a rough and irregular vibrations. You will feel your car shake and notice that the engine noise sounds different than usual. 

  • Backfire in your exhaust.


When you hear a loud backfire coming from your car’s exhaust, it can be one of the bad idle air control valve symptoms. You will hear it as a loud bang which is a common sign of some engine problems. Since it can be caused by a number of engine issues, you will have to look for any other signs that can help determine if the backfire is indeed caused by a faulty idle air control valve such as your car lurching suddenly to a stop as you take your foot off the accelerator. 


How Much Does it Cost to Fix an Idle Control Valve?


If you experience any of the bad idle air control valve symptoms, it is important that you have it checked and repaired immediately to avoid other problems from occurring. Depending on the severity of the problem, the damaged idle air control valve might need to be replaced. If you wonder how much does it cost to replace it, here’s what you need to know. 


The idle air control valve replacement cost can vary, depending on the costs of the damaged components and the labor costs of the shop you choose to do the repair. The idle air control valve can cost about $45 dollars for the standard car models while the cost can go up to $400 for the newer and high-end car models.  


As for the labor costs, it can start from $50 up to $70 per hour. It can be a bit pricey but replacing an idle air control valve should only take less than an hour to finish. However, this price can still go up if the car will need intensive diagnostics. It will be needed if you are not yet sure if the problems or symptoms are caused by a faulty idle air control valve. To determine the problem, some tests on other components of the engine should be done. 


How Do You Test an IAC valve?

Experiencing bad idle air control valve symptoms can be worrisome, thinking you will have to shell out some cash for the needed diagnostics and repair. Fortunately, there are some ways to diagnose a faulty idle air control valve. 


Keep in mind that doing do-it-yourself diagnostics should only be done if you know your way around cars and have a knowledge of the safety precautions when working on them. Depending on the make and model of your car, you may be required to use a digital multimeter or an OBD2 code reader. 

  • Using ODB2 code reader


You can use an OBD2 code reader to find out if there are any trouble codes stored in the ECU memory. To do this, you will have to connect the code reader and turn the ignition key on. Do not turn on the engine. Once you know the trouble codes, make sure that you clear them. Then you can disconnect the code reader and start the engine. 


If the check engine light is still illuminating after starting the engine, turn off the engine and proceed with the diagnostic. If the check engine light is off, drive your car for at least five minutes. If it stays off, it is an indication that you have an intermittent problem. If it comes on, proceed doing some tests. 

  • Visual inspections


You can do some visual inspections to determine the problem. Inspect the IAC wirings and look for any signs of damages, burns, deterioration, or corrosion. Check for possible shorts to ground or open circuits caused by bad insulation. You also need to check the harness connector. Make sure that the key is not in the ignition when you unplug it. Check for any loose connections, bent terminal pins, or corrosion. Since carbon build ups can cause IAC valves to become faulty, check for these build ups and make sure that everything is clean. 

  • Doing electrical tests


You can turn the ignition switch on, with the engine off, to look for the corresponding supply voltage. Consult your owner’s manual to know the supply lines. 


To do a ground test, turn the key on, with the engine off, and turn your digital multimeter dial to voltage test mode. Put one probe tip on the idle air control valve harness terminal corresponding to the supply voltage and the other probe tip on the terminal to be the ground. The voltage reading should be the same as the first test. If the reading difference is greater than ten percent, you will have to check the electrical resistance and the ground line continuity from the control valve harness to the ECU.  


Bad idle air control valve symptoms and problems can be avoided if you properly maintain your car and by taking your car to an auto service shop at least once a year to perform full diagnostics and maintain it before its components go bad. You can also extend the life of your idle air control valve by purchasing and using products to clean your IAC and throttle components. However, you need to be careful when you perform do-it-yourself cleaning and repairs.    

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