The OFFICIAL Toyota Vacuum Control System Thread

[79Corona]

I'm starting this thread for those who own Toyotas that have a gazillion vacuum hoses under the hood. You know who you are! I think we can safety say that most of these vacuum hoses/valves/dashpots are part of an attempt to save the Earth (i.e., emissions control) and a few are there for cold starts.
Anyway, there are many vacuum switch valves (VSV) used to "route" vacuum to various systems and are usually activated by an electrically operated actuator.

I'd like this thread to be both informative/educational and a place to discuss particular problems with engine vacuum systems.

For example, my 79 Corona shows a air conditioning idle-up VSV in the vacuum hose diagram, but there isn't one in the car nor does it appear there ever was. Yes, the car has an air conditioning system. The dashpot on the carb is present, but its connector for the vacuum hose shows corrosion equal to the rest of the component as though no vacuum hose was ever connected. Thoughts?