1995 Buick Regal - stalls, poor gas mileage, tach. Jumps

I've been having some problems with my 1995 Buick Regal Gran Sport (3.8L) for quite some time now, and I was hoping someone might have some suggestions on what I can replace to fix them. The reason I'm asking this is because I can't get a reading from the OBD-I connector (according to people at Autozone and a local repair shop); therefore, I have no idea what's happening. Also, I had the EGR valve replaced (about a year ago), then replaced the spark plug wires - both didn't seem to do anything.


Always does the following:

- smells like gasoline outside the car, but only when it's running (coming from exhaust)
- gets terrible gas mileage compared to several years ago


Intermittently does the following:

- "Service Engine Soon" light isn't always on - it randomly comes on after awhile and stays on until car is shut off
- stalls out when coming to a stop or after being put in neutral, but after being put in park, it often starts back up easily
- car "hiccups" (for lack of a better term) almost as if the pistons weren't firing correctly
- violently shakes up and down (whole car and tachometer) while idling, especially right after the first start-up that day
- tachometer sporadically jumps around while I'm driving at highway speeds, causing the car to change speeds (to clarify, if I take my foot off the gas pedal, the needle jumps down to 800-1000 rpm's and slows down almost as if I lightly applied the brakes; from that point, I need to press the gas pedal much more than typically needed, and it jerks the car up to 1500-2000 rpm's)


I'll keep searching the forums in the meantime - If you have any suggestions, they'd be greatly appreciated.