Idle Speed/Throttle Actuator - Electronic: Description and Operation

PURPOSE
The idle speed control system regulates the amount of bypass air entering the engine to provide for quick warm-up and to maintain idle stability and good driveability. The main system component is the Bypass Air Control Valve (BAC).

OPERATION
Air Valve
The thermowax type air valve is open when cold to allow extra bypass air into the air intake system. This raises idle speed to shorten warm-up time and ensure good driveability. As the thermowax element is heated by engine coolant, the wax expands, gradually closing the air valve.

Idle Air Control Valve
After engine warm-up, the powertrain control module engine (PCME) regulates idle speed with the idle air control valve.

CONSTRUCTION
The BAC valve consists of an air valve that functions only when the engine is cold, and a PCME regulated idle air control valve that operates throughout the engine operation range.