Idle Speed/Throttle Actuator - Electronic: Description and Operation

Idle Speed Control By-Pass Air (ISC-BPA) Valve:

PURPOSE
The Idle Speed Control By-Pass Air (ISC-BPA) valve controls idle speed by regulating quantity of throttle plate by-pass air. This permits control of cold engine fast idle, no touch start, hot engine idle speed, and engine idle load corrections.

OPERATION
For cold engine operation (below 140°F, 60°C), by-pass valve operation is controlled with a thermo wax element contracting and expanding from variations in engine coolant temperature. After engine warm-up, the ECA controls the ISC solenoid valve with a duty signal to maintain good idle quality throughout the entire engine speed and temperature range.

CONSTRUCTION
The ISC-BPA valve is two components; the by-pass air valve and the idle speed control solenoid valve.