I have a 3.0 Edge automatic, I bought it not running. There is a black plastic tube sticking out located just past the throttle valve. It is open to manifold vacuum. I have it plugged and the truck runs. What is supposed to be there?

 

There is often a vacuum source on throttle body for the EVAP system(sucks air out of fuel tank)
There should be a Vacuum Diagram on the radiator support, eliminate what you do see and what ever is left..............

 

Some folks would remove this vacuum port that runs to the gas tank fuel fume canister, thinking it would increase engine performance; it doesn't! The fumes from the gas tank are expelled into a charchol canister, then drawn into the engine intake to be burned off. No HP robbing, just some cleaner air for you and I, and our children to breathe.

In some cases, this canister failure can trigger a CEL (check engine light) code.