I was poking around the intake manifold today while considering how to install my boost gauge and I saw a hose disconnected at the passenger side of the manifold under the intercooler horn. It plugs into a nipple on the intake manifold itself and goes back behind the fuel rail. I assume this is the breather hose for the fuel pressure regulator. There's another hose above it that tees into a hard line running under the intercooler in front of the fuel rail. The other side clips into a hard line on the top of the engine mount where the other fuel lines and hoses run. What is that line? And for proper installation of a boost gauge, you're supposed to use the fuel pressure regulator line to tap into for the signal? Shouldn't I have noticed some severe running symptoms if mine was disconnected? I took a test drive after reconnecting it and I don't think I felt a difference.

The fuel pressure regulator hose is #13 in the top diagram and I believe the line I'm curious about is #6 in the bottom diagram.