91 SL2 = cuts out on acceleration, but not consistantly

Since August my car been 'dogging' out but not all the time. It happens mainly after decceleration and then when I depress the gas it just cuts out. When I pull up to a stoplight unless I keep both feet on the gas and break to prevent it from dying. This will happen for several days at a time and then run perfectly fine. I've run different gas treatments/injection cleaners through it and have also change gas dealerships. It does not pull up a code either. I took it to the Saturn dealership and since it didn't have a code they took the 'shotgun' approach - $500 worth of repairs/replacements and although when I drove it out of the shop and it did run fine for 4 weeks the same problem has returned - again with no code. I'm afraid to take it back to them for fear of spending another $500 without fixing the problem. They did a

120,000 mile service, changed plugs and wires, replaced the O2 sensor and fuel filter. It did run fine for longer than it ever had up until the other day. Any suggestions would be greatly appreciated.