Fuel By-Pass Valve (overrun cutoff valve):

The Overrun Cutoff Valve curtails fuel delivery during coasting/deceleration conditions. The overrun cutoff valve will direct excess air into the intake manifold (by-passing the air sensor plate) to stop fuel delivery when conditions of closed throttle, warm engine, and engine speed over a preset rpm are met (either coasting or decelerating). This part is also known as the Idle Actuator, Decel Valve and several other names.