When the engine is running but the vehicle is not moving, this means the engine is idling. During this time, the number of revolutions per minute (RPM) inside the engine will change. The idle air control valve is responsible for managing the engine idle speed. The valve is a major management component of the engine which will either decrease or increase the number of revolutions per minute, depending on what the current operating conditions call for. The valve is connected to the throttle body next to the intake manifold. The engine control unit is what manages the function of the valve. Based on the information it receives like engine load and temperature, it will change the speed of the idle accordingly. How an Idle Air Control Valve WorksEngine speed refers to the number of revolutions it makes per minute. This is commonly referred to as the RPM. The current operating conditions of your vehicle will cause the idle air control valve to either increase or decrease the RPM in your engine. For instance, if your vehicle has a heavy load or it is heating up too quickly, then the idle air control valve will adjust the RPM by increasing or decreasing it; respectively. This will allow the engine to handle the heavier load or cool down in each case. The engine control unit is responsible for managing the idle air control valve. When this central computer receives information about the temperature and load of the engine, it uses this information to make the proper adjustments to the idle air control valve. That way, the valve will regulate the engine RPM properly based on the information relayed from the computer. Bad Idle Air Control Valve Symptoms When you have a bad idle air control valve in your car, there are several problems and symptoms that will present themselves. If you don’t get the valve replaced immediately, your car will become undriveable. Below are the top 5 symptoms of a bad idle air control valve which you will easily notice. 1) Intermittent Idle SpeedSince the idle air control valve is supposed to manage the idle speed of the engine, a bad valve will certainly throw that out of whack. It will cause the idle speed to randomly fluctuate to different speeds rather than stay at one constant speed. The idle speed may be too high at one moment and then too low at other moments. You will clearly notice this idle speed changing by simply looking at the tachometer on the dashboard. 2) Check Engine Warning Light Whenever there is the smallest problem or issue with anything connected to the engine, it will cause the central computer to activate the check engine warning light on the dashboard. A bad idle air control valve could certainly be one reason for this to happen. If the number of revolutions per minute seems peculiar to the engine control unit, it will let you know by activating the warning light. Of course, there could be a whole list of other reasons for the warning light to come on too. In any case, you should take your vehicle to the auto shop to get it checked out at once. 3) Rough IdlingA normal healthy idle air control valve will provide smooth idling in your vehicle. But if the valve goes bad for any reason, the idling will go from smooth to rough. A rough idle will result in intense vibrations forming whenever your vehicle is stopped with the engine running. Since less air will be going into the engine during its idle state, the car will react by shaking profusely. 4) Engine StallingIf you experience engine stalling from a bad idle air control valve, then you won’t be able to drive your vehicle at all. As soon as you start your car, the idle air control valve will immediately malfunction. If you happen to be away from home and this happens, the stalling will happen every couple of minutes in the beginning. You should be able to make it to the nearest mechanic in time before the engine stalls completely. 5) Load Causes StallingSometimes the engine stalling will happen on its own while other times, increasing the load on the engine will cause it to stall. For example, if you turn on your heater or air conditioner when you have a bad idle air control valve, then your engine will probably stall immediately afterward. The steering wheel might also feel like it’s being dragged to one side too. To temporarily fix this problem, just turn off your heater or air conditioner to reduce the load. Then let the engine cool for a couple of minutes. Idle Air Control Valve Replacement CostIf a voltmeter shows a reading outside of the normal range, then you need to purchase a new idle air control valve. Unless you know a lot about auto repair, you’ll need to pay a mechanic to perform the replacement job. That means you’ll need to pay both parts and labor costs. The average replacement cost of an idle air control valve is between $120 and $500. The parts could cost anywhere from $45 to more than $400, while the labor is only around $70. Of course, the labor cost really depends on the hourly rate of the mechanic. Since this job should not take more than 1 hour to perform, don’t expect the cost to be too high. Certain vehicles are more complicated to work with than others, so that is a factor too.