Idle Speed Control System
WARNING: This page is about a different car, the 1996 Toyota Corolla. However, it is still accessible from the selected car via links, so may be relevant.
Engine Control Module (ECM) is programmed with engine idle speed values. Idle air control system provides a stable idle speed when engine is cold or idle speed decreases due to electrical load. The Engine Control Module (ECM) uses various input signals to maintain proper idle speed by controlling Idle Air Control (IAC) valve.