Corolla/FX L4-1587cc 4A SOHC (1984)
Throttle Opener: 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.
4A-C & 4A-LC ENGINES COROLLA FRONT WHEEL DRIVE
These models use a dual diaphragm throttle positioner in order to open the throttle slightly during deceleration and at idle when vehicle electrical loads
cause idle speed to drop. Manifold vacuum is applied directly to the positioner outer port while ported vacuum is applied to the inner diaphragm
chamber. Vacuum must be applied to both diaphragm chambers to retract the positioner and allow the throttle to close fully.
During normal idle conditions, vacuum is applied to both diaphragm chambers and the throttle positioner is retracted. When heavy electrical loads are
placed on the alternator the Vacuum Switching Valve (VSV) circuit is energized, the VSV opens venting the outer diaphragm chamber to atmosphere
and spring tension extends the positioner to the first step raising the idle speed. When electrical loads are decreased, the VSV is de-energized and
vacuum retracts the positioner.
During normal running, vacuum in the inner diaphragm chamber is nearly equal to atmospheric pressure and spring tension extends the positioner. When
the throttle is suddenly closed, the resulting high vacuum is delayed from reaching the inner chamber by a Vacuum Transmitting Valve (VTV). This
delay allows the positioner to remain extended briefly, then slowly retract allowing the throttle to close.
