Your car contains hundreds of different components to make it work properly.
All engine components are interdependent and contribute to the smooth operation of the engine. Of the many parts and sensors in the engine, one component, called the idle air control valve, is critical to the engine. Its task is quite simple, but crucial for the smooth operation of the engine.
The idle air control valve is normally installed in engines with fuel injection. A similar device is found in carburetor vehicles and is called an idle speed control actuator.
The difference between the two is that the IAC is controlled by the car’s ECU, which is present in modern fuel-injected cars.
In this article we will discuss the operation of the idle speed control, the most common symptoms of a bad idle speed control valve and the replacement costs.
Signs of a Faulty Idle Control Valve
Like other sensors and components in a car, the idle air valve also breaks down after years in a hot engine compartment. It can either get clogged or stop working completely. If this happens, you will immediately notice that your car no longer runs smoothly in neutral and sometimes even comes to a halt. In addition, your car may stutter a little when refueling. If the idle speed control valve is not working properly, you may have to keep your foot on the accelerator to prevent the engine from stalling.
Here are some signs you should look for to determine if your IAC valve is failing:
1. Rough/Jumpy Idle
Because the idle control valve ensures that your engine idles smoothly, a faulty idle control valve will cause your idle to either jump up and down in RPM or get stuck at too high or too low RPM. You can also expect your idle speed to jump up and down.
2. Check Engine Light
The engine control unit controls all sensors of your engine in real time. If the engine control unit receives faulty values from a sensor, it stores them as an error code. If the problem occurs more than once, the engine control unit lights up the Check Engine Light on your dashboard. If you notice this, read the error codes with an OBD2 scanner.
3. Engine Stalling
If the idle control valve gets stuck in a closed position, problems may occur, such as your engine stalling at idle or needing to accelerate a little to keep it running continuously. If this happens to you, take the idle control valve apart and clean it.
4. Rough Acceleration
The idle control valves may also cause your throttle body to incorrectly calculate the air entering the engine. In some cases, you may expect problems with a poor idle control valve even at higher RPMs using these functions.
What is the function of the Idle Control Valve (IAC)?
The IAC is a relatively small device, and it is a simple valve for controlling the airflow to the engine. The unit is installed between the air intake systems in such a way that either a small amount of air reaches the engine when the throttle is closed, or the throttle or butterfly valve can take over the air flow to the engine. The idle control valve has a servo that pushes and pulls a piston, with a cavity inside the housing that either blocks or exposes when the servo pushes the piston.
The idle speed is controlled by signals from the vehicle’s computer system that tells the idle control valve how much it should move. The idle control valve is designed to allow a small amount of air to flow to the engine even when the throttle or butterfly valve is fully closed.
Why is the air idle control valve so crucial to the engine?
To keep the engine running, the engine needs a constant supply of air that mixes with the fuel. An engine typically idles at about 500 to 700 RPM, which is essential because a little fuel is needed to keep the car running longer without overloading the engine, and consequently the engine produces less heat. To maintain the engine speed in the range of 500 to 700 RPM, the butterfly valve on vehicles with manual fuel injection, or the throttle body on vehicles with fuel injection, must be closed almost to the “complete stop” position. The positioning must be as accurate as possible so that the speed needles do not jump too much and remain largely constant.
The problem with the almost closed throttle valve, however, is that the RPM of the engine is not constant and needs to be adjusted in real-time to keep the engine running. This is because both the air pressure and the temperature of the atmospheric air fluctuate, which can cause fluctuations for the engine. This can cause the engine to stall frequently.
This is where the idle air control valve comes into play. The throttle or butterfly valve closes and completely blocks the flow of air to the engine, but the idle air control valve opens slightly to allow a small amount of air into the engine to prevent stalling. Because the idle control valve is controlled by electrical signals from the vehicle’s ECU, the ECU constantly gives signals to the idle control valve, which it must adjust according to the temperature of the incoming air and its pressure to keep the engine at optimum idle speed. In this way, the ECU can control the engine speed via the idle control valve, regardless of the load on the engine.
The Idle control valve compensates for the load of the AC compressor
For example, when you turn on your air conditioner, your AC compressor starts up and puts a little load on the engine through the belt that drives the compressor pulley. This is not a problem if you are operating at 1,500 to 2,000 rpm, but if you are not driving and the car is at a dead point without the idle air control valve, the engine would die or start shaking violently as soon as the air conditioning is turned on. You would have to put your foot on the accelerator to keep the car from stalling. The idle control valve quickly adjusts the position of the piston to allow more air into the engine, bypassing the throttle or butterfly valve and compensating for the loss of power when the air conditioning is switched on. Just as turning the steering on a car with power steering puts additional strain on the engine, this is compensated for by letting more air in through the idle control valve.
Similarly, if the extra load on the engine is removed, this would result in the engine speed increasing above 1000 RPM. The idle control valve then adjusts itself so that the air intake is closed to the point where the extra air is no longer needed.
Idle Control Valve Replacement Cost
The replacement cost of an idle control valve varies by make and model, the valve can cost between $50 and $300. The valve can often be replaced quite easily, and you can avoid labor costs between $50-250 if you don’t have it done by a mechanic.
This part is small, but often you can clean and lubricate it if it gets stuck. Sometimes the valve itself is functional but limited because some debris has settled in the servo path, which could prevent it from moving freely. In this case it is sufficient to service the valve only from the outside. Idle valves can often be removed naturally, so you should first check the valve for obvious signs of clogging or deposits.
However, if you find that the servo does not move at all when given certain signals, it is time to replace it.