wbtt

hello - I've got a 1993 300ZX TT that is running very rough. This happened once before and it was just a vacuum line that came loose, so I went looking for loose lines. I found what looks to be a vacuum port with no line attached on the the engine - passenger side back - but I can't find any loose vacuum lines. I looked in the FSM but was unable to ID it. Does anyone know what line should go on this port? I've attached a picture.