I just finished, but it looks like there is a fitting that a vaccum hose belongs on. It's right under the intake tube. I don't remember anything on there from stock. What is that tube?

On my 04 there is a metal tube, approx .25" dia. with no hose connected. It came that way.

I had the same thing on my '03. If this is similar to what I have seen on other vehicles and what I've been told, it's something that is used to balance out manifold pressure with atmospheric pressure. Not too sure about that...might want to ask one of the Nissan Gurus.

It is your seleniod tube. My 03 had a hose so I attached the factory hose to the FIPK one. If your X doesn't have one then you should have a plastic plug to plug up the hole that came with your kit.