1987 1/2 Models

At ambient temperatures greater than 50°F (10°C) and engine coolant temperatures greater than 128°F (53.3°C), the 4-port Ported Vacuum Switch (PVS) will allow manifold vacuum to enter the switching control diaphragm of the air diverter valve.

At idle and part throttle, the manifold vacuum signal is strong enough to cause the switching control diaphragm to operate, rerouting air pump output from the exhaust manifold to the catalytic converter.

At wide open throttle, the loss of manifold vacuum to both the bypass control diaphragm and the switching control diaphragm will cause all air pump output to be dumped into the atmosphere.