An Idle Air Control (IAC) Valve works by controlling the flow of air into the Intake Manifold. The IAC adjusts the amount of airflow entering the Engine to ensure that it can maintain its RPM level when idling. This process occurs in response to signals from Sensors located in various parts of the vehicle, such as the throttle position sensor or mass airflow sensor. When these sensors detect changes in conditions such as load or temperature, they send signals to the computer that controls the IAC valve, which then adjusts accordingly to maintain a steady idle speed.
SYMPTOMS OF A BAD IDLE AIR CONTROL VALVE (IACV)
If your vehicle has a faulty or worn-out Idle Air Control Valve (IACV), there are several signs you might be able to spot that indicate something isn't quite right with your car's idle system. These include: 
• Erratic Idle Speed – If your car's idle speed changes drastically or jumps around for no apparent reason then it could be due to a faulty IACV.
• Unusually High RPMs – If your vehicle's RPMs remain high even after coming to a stop then it could be due to an issue with your IACV. You may also find that your car stalls out shortly after coming to a stop as well.
• Check Engine Light – A malfunctioning IACV can trigger your vehicle’s check engine light warning, so keep an eye out for this as well if you suspect there might be something wrong with your car’s idle system. An Idle Air Control Valve (IACV) is an important component of any vehicle’s engine because it helps regulate the amount of air entering into the engine during idle periods. Signs that may indicate something wrong with yours include erratic idle speed, unusually high RPMs, and activation of your check engine light warning signal. If you believe there might be something wrong with your car's IACV, take it in for service as soon as possible so any potential issues can be addressed before they become major problems down the line.