In the 123 manual - "checking ac vacuum system" - the vac diagrams show a "throttle valve" in line (vac line) just before the recirc vac actuator - a couple of the other pods have them too. (85 300TD California) - By the way, my system does not have a check valve at the center vent actuator. Does anyone know the importance of this throttle valve. (It is a small plastic piece inside the rubber vac hose.

Thanks Steve