1987 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 ported vacuum to enter the switching control diaphragm of the air diverter valve. At idle, the switching control diaphragm does not operate, sending all air pump output into the exhaust manifold.

At part throttle, the ported vacuum signal is strong enough to cause the switching control diaphragm to operate. This will reroute air pump output from the exhaust manifold to the catalytic converter. At wide open throttle, the loss of manifold vacuum to the bypass control diaphragm of the air diverter valve will cause air pump output to be dumped into the atmosphere.