What connects to the intake manifold where the throttle body assembly mounts to the intake manifold?

There is a vacuum line the goes from the valve body to the brake booster. Below are the instructions that show the line along with how to remove the intake manifold and reinstall in case you need it. Check out the diagrams (below). Please let us know if you need anything else to get the problem fixed.

It looks like that goes to the EVAP canister control solenoid, here is a diagram so you can see. Check out the diagrams (below). Please let us know what happens.

Do you have any vacuum lines that are lose under the hood, maybe it was just a plugged port?

I would plug the port and see what happens.