I've asked in a few automotive forums. Here's my post from them:

I have been working on an 87 Jetta that I just purchased for $250 Canadian. I have an 86 for parts. Started with the minor stuff, like replacing the window regulators, installing a new drive belt, swapping out the window washer pump etc but I noticed there was a hose disconnected in the 87 and had a look at the 86 and saw that on the other end of this part, someone had sawed off the pipe leading out of it and plugged up where it should have been connected with a bolt!
I thought I'd consult the service manual I have to see just what this part was that the car seems to run fine without. My 86 ran for 5 years with it disconnected and the 87 runs fine without it. However, I cannot for the life of me find it in the manual or in online VW parts catalogues. I'm guessing the part looks different now in 07 than it did in the late 80s. Can someone please identify it for me?

I'm really not a helpless female. I do alot of my own work on these cars. But this one has me stumped.

Here's a link to some photos of the UFO part. lol

My best guess so far has been that it's the vacuum advance unit or the fuel pressure regulator but I'm really not sure.
http://www.facebook.com/album.php?ai...p;id=584996953 or see the pic below. The UFO part is circled in green for your mystery solving pleasure.

 

Nevermind, got it! EGR valve. Whew.

 

Loving your avatar. [sm=Flahssssss.gif]Hahahaha!