I have a 1994 Chevy Cavalier 3.1 MFI, 3 speed auto, w/AC, (204,000 miles). It occasionally hesitates and stalls like it is not getting fuel, but will immediately restart. It is more apt to do this after about 20-30 minutes of stop and go driving, especially when starting out at a stoplight. A few times, it seemed like it was going to die at highway speeds. Otherwise, it runs OK. I recently tuned it up, changing the O2 sensor, plugs and wires, air filter, and oil and filter. I changed the fuel filter which was full of crap. Added some injector cleaner and drygas. Seemed to be ok for about 2 weeks, then the problem started again. Any ideas on what may be causing this problem.
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08/03
Found out the O2 sensor was bad, (after 3 months!). Changed it out. The next day the beast stalled out and would not start other than for a couple of seconds after cranking the starter. Had the car flatbedded to the garage. It did not start for the mechanic on the first try, but started up and ran good after he shot some ether into the air intake. They ran it (idling) for 1 hour with the a/c going full blast to try to get it to stall. They checked for vacuum leaks, bad connections, bad fuel pump relay, etc. Could not find anything, and could not get it to stall. Only suggestion was to loosen up the gas cap as the vent hole may be plugged and could be causing a vacuum in the tank cutting off the flow of gas.

Took his advice, ran the car for 150 miles in the 100 degree heat wave with the a/c on with no problems.

Anyone have a similar problem? Any further suggestions?