Throttle Positioner System: Operation
The TP system is vacuum controlled. When the engine is cold, the TVS valve is open and holds the positioner in a set position. When the engine is warm, the throttle open and vacuum at TP port is low, the positioner is in a set position. When the throttle is released, as during deceleration, the positioner keeps it from closing completely until vacuum bleeds through the VTV. The high vacuum present at the TP port will then pull the positioner back and allow the throttle to close completely.