I have one of those "my mechanic can't fix it because he has no idea what's wrong" problems...
My car is a '96 Mystique GS.
The symptoms are as follows:
-On acceleration, engine is reluctant to rev, and it sounds like there's not enough fuel going to the engine?
-If the above happens, flooring it gets rid of the problem momentarily.
-Occasionally dies.
The car was in the shop for the whole week now, just picked it up Friday morning, and instead of the intermittent problem gone, it is now doing it all the time!

The mechanic replaced :
-The whole manifold/precat/flex assembly,
-The O2 sensor
He said he test drove it without any problems , but I have a hard time believing that, as the car stalled less then 10' from the place when I got it back.
Now I'm out ~$1000 and the condition is worse than ever...

I think I'll have to fix this myself, there's no way I'll be taking it back come Monday...

Thanks in advance for any advice!