I went through the same thing this past Friday. Here is another thread on the same subject.
I also cleaned out the vacuum hose connections on the plenum. There seemed to be <Chevy Chase>g00k</Chevy Chase> all over them. I suspect that this is due to the oil making it's way into the plenum from the PCV but that's just my guess
This may be a sign of a faulty fuel pressure regulator, you can find this part located at the left hand side of the engine compartment next to the plastic fuel injector rail.
Here's a pic of the FPR on the 2.0L:
Just ignore that plugged up vacuum port...gutting the airbox eliminated the need for it
[Modified by bajan01, 6:09 PM 3-10-2003]