What's this thing that is hissing?
 

Recently got a 2000 XJ with the 4L I6. Don't know much about cars really so forgive the stupid question. So when I was under my hood, I heard a hissing noise. Looked around and found this silver nipple lookin thing on the right side of the engine:

https://cimg1.ibsrv.net/gimg/www.che...32c2f90fa9.jpg
https://cimg5.ibsrv.net/gimg/www.che...6e3506a06f.jpg


It's a vacuum of some sort, so I am guessing there is supposed to some kind of hose here. Can someone tell me what this is for, if there should be a hose attached, and if so, how problematic is it that there is no hose?

I have that same vacuum port on my 2000. I couldn't find anything to connect to it so I just covered it.

Take a look at this thread.
http://www.jeepforum.com/forum/f11/w...sport-1803673/

Thanks for that link! I'll try throwing a cap on it and seeing if that works.

if that has no plug itll idle high. I just threw a plug on it and called it a day and hasnt acted up since. I have no clue what its for and dont think it serves a purpose.

On a 2000 with CA Emissions all 3 of the nipples off the intake manifold are used. On a 2000 with Federal emissions one is not. Can't remember which one though. So I am guessing you have a Federal Emissions one and that is the one that gets capped off.

Stick your finger over it and the engine will run differently.

It usually has a cap on it. You can get a pack of generic caps at most auto parts stores. I found mine sitting underneath the computer.