•  The BAC valve consists of the air valve, which functions only during cold engine conditions; and the IAC valve, which works throughout the entire engine speed range.

•  The air valve increases idle speed during cold conditions to quickly warm up engine. The air valve consists of the thermo wax and the valve. Engine coolant is directed around the thermo wax.

•  When the engine coolant temperature is low, the thermo wax contracts and the air valve opens.

•  When the engine coolant temperature rises, the thermo wax expands and the air valve closes gradually.

•  In order to ensure idle smoothness for all operating conditions, the IAC valve carefully controls the bypass air amount.

•  When the engine is cold, besides bypass air flowing through the air valve, air also flows through the IAC valve to maintain the target engine speed set the PCM.

•  After warming up the engine, only the IAC valve controls the bypass air amount to maintain the target idle speed.