Idle Control System Diagram

The idle speed of the engine is controlled by the Idle Air Control (IAC) valve:

• After the engine starts, the IAC valve opens for a certain time. The amount of air is increased to raise the idle speed by about 150-300 RPM.
• When the engine coolant temperature is low, the IAC valve is opened to obtain the proper fast idle speed. The amount of bypassed air is thus controlled in relation to engine coolant temperature.
  Fig 1: Identifying Idle Control System Functional Layout

  Courtesy of AMERICAN HONDA MOTOR CO., INC.