Idle Control Valves

The By-Pass Air Control (BAC) valve contains an air valve. Engine coolant is directed around air valve warming thermowax. When engine coolant temperature is less than 122°F (50°C), wax is contracted and engine idles fast. When coolant temperature is more than 122°F (50°C), wax is fully expanded, closing valve.

The Idle Speed Control (ISC) valve controls air by-pass amount during warm engine operation. The ISC valve compensates for all engine loads during warm engine operation to maintain a preset idle RPM. The ISC is controlled by the PCM.

The Accelerated Warm-Up System (AWS) valve is open at temperature less than 104°F (40°C). At temperature greater than 104°F (40°C), valve is closed, preventing rough idle under some cold engine conditions.