It's the top hose that's coming off of the UIM on the left side. What is it?

 

Since you don't have a picture to point at it, I'm assuming you are referring to the brake booster line. Does it run to a hardline on the firewall?

 

A pic would be helpful. Sounds like a BOV or boost gauge hose, depending on your mods...

EDIT: Oh yeah, or maybe the brake booster hose.

 

Sorry for no pic guys, my camera's not wanting to cooperate. It's actually not the top line, it's the middle. There are three hoses coming off of the left side of the UIM. The very top is a larger diameter hose with two smaller ones equally spaced down from it. The middle hose runs along the firewall towards the driver's side and I don't know where to. I only ask because this hose is very loose at the UIM, it takes absolutely no force at all to remove it.

 

Sounds like a hose that goes to an aftermarket boost gauge, since it's running along the firewall and headed for the drivers side, does it go through the firewall ? You can probably trim off a half inch or so and that may tighten it up, or add a tywrap and see if that does it.