79 300sd vacuum line question

[jabbene]

My question in concerning a vacuum line that I cannot figure where it should connect. There is a Y that comes out of the top of the VCV. One connection couples with another Y. The other is a black line that goes left behind the valve cover and is just hanging loose under the engine compartment.

The transmission is also shifting rough and I was hoping this was related to this disconnected vacuum line.

I have looked at many diagrams and cannot figure it out. FYI this is not the vent line that goes under the dash. I am fairly certain this line should connect somewhere.

If anyone could help I would really appreciate it with any pictures of where this should connect. Thank you.