V 2500 P/U 4WD V8-350 5.7L (1987)
Idle Speed/Throttle Actuator - Electronic: Description and Operation
IAC Valve Operation And Fuel Pressure Regulation
Engine idle speed is computer controlled by signals to the Idle Air Control (IAC) valve mounted on the throttle body. The IAC valve regulates idle speed
by moving a pintle valve in and out, varying air flow through a passage bypassing the throttle valve. The more air that is allowed to bypass the throttle
valve, the faster the idle speed. The ECM sends voltage pulses to the IAC motor windings causing the IAC motor shaft to move a given distance for each
pulse, (referred to as IAC counts). The number of IAC counts can be read on a Scan tool display. 0 counts corresponds to fully closed passage, while 140
counts or more (depending on application) corresponds to full flow. The ECM monitors idle speed and increases the IAC counts if the idle speed is too
slow. If the idle speed is too fast, IAC counts will be decreased.
