Idle Speed/Throttle Actuator - Mechanical: Description and Operation

The Throttle Positioner (TP) system uses a diaphragm type actuator, connected to the throttle linkage, to prevent complete closing of the throttle during high vacuum conditions such as deceleration and/or at idle. Actuator operation is controlled by ported vacuum signals, modified in a variety of ways.




3A-C, 3E & 4A-C ENGINES EXC. COROLLA FRONT WHEEL DRIVE

At idle, intake manifold vacuum is present at the throttle position port, the throttle positioner diaphragm is pulled by this vacuum, and the throttle valve is at idle speed position. Under normal operating conditions vacuum at throttle positioner port is nearly equal to atmospheric pressure, the throttle positioner diaphragm is pushed out by the diaphragm spring, and the throttle valve is in the high speed position. During deceleration, intake manifold vacuum is present at the throttle positioner port, the throttle position diaphragm is pulled by this vacuum after a delay caused by the vacuum transmitting valve, and due to this delay the throttle valve slightly opens and slowly closes to the idling position.