From the book:
Boost Control System
The boost control system regulates induction boost pressure during rapid decelearation, under very high engine load situations and anytime reverse gear is selected.
Under most conditions, the PCM commands the boost control solenoid to operate at 100% duty cycle ("ON"), keeping the solenoid valve closed and allowing only inlet vacuum to control the position of the bypass valve. At idle, full inlet vacuum applied to one side of the bypass valve actuator diaphragm counteracts spring tension to hold bypass valve open. As engine load increases, reduced vacuum acts upon the spring tension in the bypass valve actuator, causing the bypass valve to close and increasing boost pressure. When reduced boost pressure is desired, the PCM commands the boost control solenoid to operate at 0% duty cycle ("OFF"). This opens the solenoid valve and allows boost presure from the intake manifold to counteract the spring tension in the bypass valve actuator, opening the bypass valve and recirculating excess boost pressure back to the supercharger inlet. With reverse gear selected, the PCM commands the boost control solenoid to operate at 0% duty cycle ("OFF") at all times.
Results of incorrect operation
An open CKT 922 or boost control solenoid valve stuck open will cause reduced engine power, especially during wide open throttle operation.
CKT 922 shorted to ground, boost control solenoid valve stuck closed or a restriction in the boost source or signal hoses will cause full boost to be commanded at all times and a possible overboost condition during high engine load situations.
A restriction in the vacuum signal hose to the bypass valve actuator will cause a rough idle and reduced fuel economy.
Now we're all on the same page. I'm curious what exactly it considers very high engine load...
Stuff got done.