Servo Unit

The servo unit consists of a vacuum operated diaphragm, a normally open solenoid valve that vents diaphragm chamber to atmosphere, a normally closed solenoid valve that connects diaphragm chamber to vacuum source, and a variable inductance position sensor. Servo operates throttle position in response to signals from control module as follows:

Steady Cruise State

Both vacuum and vent valves are closed. Servo has constant vacuum on diaphragm and places no-flow requirement on vacuum source. Vacuum is trapped in diaphragm.

Vehicle Losing Speed

Control module energizes vacuum solenoid to open vacuum valve to vacuum source. This increases vacuum level in servo to increase throttle opening. Vent remains closed.

Vehicle Gaining Speed

Control module de-energizes vent solenoid to open vent valve to atmosphere which reduces vacuum in servo and allows throttle return spring to decrease throttle opening. Vacuum valve remains closed.