The Idle Air Control, referred to as the IAC, is actually a variable flow valve that bleeds air into the intake manifold. It’s purpose is to provide air during startup, raise the idle speed during engine warm up, stabilize idle speed, prevent stalling, act as a damper during deceleration, and provide additional air during hard acceleration. Although optional, it’s suggested it be included in all new installations and is a must on engines with air conditioning or automatic transmissions to maintain a steady or increased idle speed. We recommend adding an IAC whenever possible.