That line goes to the smog system that goes to the back of the heads. I think it opens and closes that valve right there which allows the air(smog) pump to pump the air from the back of the heads thru the pump and down to the H pipe. The reason u dont notice any difference is because we all know smog does nothing for performance. So u can either leave it the way it is or redo the whole vacuum tree with rubber vacuum hose from a hardware store. Its really easy and allows you to hook up guages ect alot easier. I would redo it, because chances are another one of those little vacuum hoses is going to break sooner or later and u will get a crap idle because of a vacuum leak.