What's the difference between an idle control valve and a stepper motor?

The Idle Air Control (IAC) Valve is a particular type of stepper motor used in automotive engine applications. A stepper motor is basically an electrical device that controls a plunger, so that the plunger can be a precisely positioned to multiple different depths. 256 different positions in most applications. An IAC Valve adds a pintle, which is matched to an orifice in the throttle body of a Throttle Body Injection (TBI) system, or the intake plenum of a Multi-Port Fuel Injection (MFI) system. This is used to regulate the amount of air flowing into the engine, separately from a throttle valve which is controlled by the accelerator pedal. This helps to control the idle speed of the engine under varying conditions, such as whether the air conditioning is on, the power steering is being used while parking or coasting, temperature variations, and so forth. It's why you no longer have to press the pedal when you start a modern car with a cold engine. For a highly technical explanation ...  more