I have had my 92 prelude for just over a week now, and it has a jdm f22b motor swapped in. There is a vacuum line going from the middle of the valve cover, between the middle 2 cylinders, that runs to the intake manifold. This line is not secured at the valve cover, but almost looks as if it should clip onto the cover itself. The line coming from the IM is vacuum, but the line coming from the VC has pressure. The engine idles choppy when they are connected, but when I disconnect them, it seems to hold fine at 1k, and sounds ok. Can someone tell me what this vacuum line is for, and if it should be connected, even though the car runs better when it is disconnected?

I have been told that the engine I have (JDM F22B) is very similar to a usdm h23a1, but looking at a vacuum diagram for the h23a1, I am unable to find the line I am referring to.