Symptoms of a Bad Idle Air Control Valve

If the 'Check Engine' indicator on your vehicle glows continuously, a possible cause may be a malfunction in the idle air control valve. This Buzzle article tries to list down the possible signs and symptoms of a bad idle air control valve.
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Sign of a bad idle air control valve
Did You Know?
You can use a throttle body cleaner spray to clean the idle air control valve effectively.
An idle air control valve is placed in the throttle of your vehicle, and ensures smooth idling of the vehicle by regulating the amount of air that reaches the engine. In case this valve goes bad, as its name suggests, the immediate effect will be observed on the vehicle's idling speed. However, certain other issues may also be observed, like an idling vehicle stalling when the AC is switched on, and the like. Such sudden changes in the engine RPM can have long-lasting effects on the life and performance of the engine. Hence, we, at Buzzle, have highlighted the signs of a faulty IAC, and the methods on how to check for a bad idle air control valve.

Variation in Idling RPM
It is a known fact that when you accelerate, the engine RPM increases, and once you step off the gas, the RPM slowly returns to the normal idling speed. However, when the engine RPM drops below the normal range of 800 RPM (for most cars), it is more than likely that you are dealing with an IAC valve problem. In cases where this valve is clogged or is nearing its replacement age, your vehicle will stall instead of idling after the release of the throttle.

Idling is Not Smooth
The main function of the IAC valve is to ensure that your vehicle idles smoothly. However with a bad IAC valve, this idling will be rough. You will experience heavy vibration (shuddering) when you idle the car. As the valve has gone bad, there will be no/very little air flow to the engine, when you idle the car. Thus, your car will shake, vibrate, and may also make a loud noise while idling. Due to this rough idling, the next time you start the engine (the car), you will notice that the car stalls immediately after starting. Your car's IAC valve might be clogged with carbon debris, and due to this, the valve might not open sufficiently enough to let the air to pass through it.

Engine Stalls Due to Load
Under normal conditions, when your car is idling, if you turn on the AC or heater, your vehicle will still idle smoothly. However, if the IAC valve is faulty, your engine will stall the moment you increase the load (AC or heater) on an idling engine. You will also experience a drag on the steering wheel once the AC is switched on. To restart the engine in such situations, you should turn off the load and wait for few minutes for the engine to cool down before you crank it up again.

'Check Engine' Light is On
The most obvious sign of engine malfunction is the blinking of the 'Check Engine' light. This indicator, which is placed on your car's dashboard, indicates that your vehicle's engine has problems. You need to examine the error code by using an OBD II scanner. For this, you need to connect the scanner to the OBD II connector which is placed on the driver's side. Turn the key on, and let the scanner analyze your vehicle. If it returns a code 11 error, your faulty idle air control valve problem is confirmed. You can then replace the old IAC valve with a new one in case cleaning the same doesn't solve your problem.

How to Check if the IAC Valve is Healthy?
You can check the health of the valve by checking its resistance. When you disconnect the IAC valve, connect an ohmmeter to pins 2 and 3 of the valve. If you get a resistance value between 10-14 ohms, it indicates a functional IAC valve. Now, connect the ohmmeter to pins 1 and 2. If you don't get a resistance value between 10-14 ohms, this means, the IAC valve needs a replacement.

The Solution
Now, when you know that your idle air control valve is bad and needs repairs, the best solution, besides a replacement, is to clean the IAC valve thoroughly. You need to remove the IAC valve and spray it with throttle body cleaner. The carbon gunk that is stuck inside the valve will start to come off. You can continue spraying until the valve looks clean. However, do remember to drain out any excess fluid that is present inside the valve. You can also clean the throttle body with this cleaner. Once everything looks clean, you can reassemble the IAC valve. This time around, your car will start rough.

However, if you are experiencing problems even after cleaning the valve, you need to replace the valve.

You can click here, to know more about the functioning of the IAC valve.

In case the idle air control valve is not functioning properly, your car will have abnormal idling. Highly fluctuating idling or sporadic stalling, this can further deteriorate the engine life and performance. Thus, it is necessary to fix this problem as early as possible. If you are not a pro in such tasks, take your car to a mechanic to replace the IAC valve.
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Published: May 2, 2014
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