Fast Idle Control Device (FICD)
WARNING: This page is about a different car, the 2001 Subaru Impreza and 2000 Subaru Impreza. However, it is still accessible from the selected car via links, so may be relevant.
The FICD, which is a by-pass air control solenoid, increases engine idle speed when A/C compressor is turned on. Engine Control Module (ECM) activates the by-pass air control solenoid. This solenoid controls the amount of by-pass air flowing through throttle body. This is in relation to signal emitted from A/C switch so that proper idle speed specified for each engine load is achieved.