Idle Speed/Throttle Actuator - Electronic: Description and Operation

Idle Speed Control System:

PURPOSE
System controls the amount of bypass air through the throttle body, improving warm-up and idle quality.

LOCATION
Idle speed control (ISC) valve is on bottom of throttle body. Air valve is on bottom of dynamic chamber.

OPERATION
The air valve is the thermowax type that is open when cold to allow extra bypass air into the dynamic chamber. 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. After engine warm-up, the ECU controls the ISC valve with a duty signal to maintain good idle quality under across the range of operating conditions.

CONSTRUCTION
System consists of two valves: the air valve functions only when the engine is cold, and the ECU regulated ISC valve operates throughout the engine operating range.