My sick bora :-( Any ideas. help!

[NEILS-GTI-MK3]

I'm suffering from bad mpg at the mo, and i think it's running rich.
What can cause this?  it a 99 2.0 bora.

And if i disconnect a small vacum pipe off the inlet manifold, it seams to idel abit better.
This is a pipe that goes to a round thing that sit on the left side of the injector rail.
 Not sure what to call it.  when it's connected it idels low. help?

The air mass meter has been replaced, so shouldn't be that.

any help on this please 

[topher]

That particular engine is notorious for bad mpg.. they're also known to drink a lot of oil. Try putting it on a diet of redex for the next couple of refills.. see if it helps.