Missing vacuum hose, I cannot find where it goes

I have a hose missing on the intake that runs into the throttle body there are two nipples side-by-side. The top one has a hose running into the valve cover the bottom nipple has no hose and is sucking air making the car run bad, but I cannot find where I need to run a hose at from that nipple. I checked the diagram, and it was no help and if I plug the nipple the car shuts off. I don’t have a pic of mine, but I’ll put a picture in of what I’m talking about. If someone could help me with this I would greatly appreciate it.