By-Pass Air Control (BAC) Valve

The BAC valve contains an air valve and Idle Speed Control (ISC) valve. Engine coolant is directed around the air valve warming up the thermo wax. When engine coolant temperature is less than 122°F (50°C), the wax is contracted and the engine idles fast. When coolant temperature is more than 122°F (50°C), the wax is fully expanded, closing valve.

The Idle Speed Control (ISC) valve controls air by-pass amount during cold and warm engine operation. During cold engine operation, the ISC valve opens, raising fast idle speed to a predetermined RPM. The ISC valve also compensates for all engine loads during warm engine operation to maintain a preset idle RPM. The ISC valve is controlled by the ECU.