PL720 2WD L4-1952cc 2.0L SOHC (Z20) (1985)
This system consists of a boost control unit, made up of a boost control valve and diaphragm, which acts as a manifold vacuum sensor, and a bypass air
control unit, made up of a bypass air control valve and diaphragm, which acts as an actuator.
The boost control unit senses the manifold vacuum. When the level of the manifold vacuum exceeds a predetermined value, the boost control valve
opens and transmits manifold vacuum to the air bypass control unit. The manifold vacuum then pulls diaphragm II and opens the bypass air control
valve, causing air to be bypassed to the intake manifold. Upon completion of air bypass, manifold vacuum is lowered. This results in the closing of the
boost control valve and then the closing of the air control valve. This system operates in a tightly controlled circuit to keep manifold vacuum very close
to predetermined value during deceleration.