Help Identifying Part, Please

This will show my ignorance, but y'all have helped me in the past and I am stumped.

There is a metal tube-like part next to or attached to the manifold of my 87 Jetta. The part was capped with a rubber tip, but the rubber was old and it crumbled away. I would like to replace the tip, but I do not know what I am looking at/for. I cannot find it in my Chilton's.
Photos available at http://www.geocities.com/stevewebster_56/engine-with-hot-tube.html
(sorry 'bout no hyper link, not finding a way to do it... copy and paste will work)
Is the missing tip the reason the engine sounds much louder now?
Is there something more I should know about this part?
Thanks!!!!
Webster

An alternative...
Is there a good blow up diagram / photo with parts identification on the web?

btw, the link does work. It is to our personal page at yahoo where I have uploaded pix of the engine.

thanks,
still hangin'.

I'm not absolutely sure what it's for. I read once a few years ago, but can't remember. It goes down to the exhaust manifold and I believe it's used to test emissions. I'd find a new rubber cap for it from the dealership. It shouldn't be more than $10.

Thank you very much!

Thats the egr tube, its really not very important past emissions.

if your egr isnt working than you will fail emissions horribly in the NoX reigion.