1993 Cadillac Deville car is stalling at idle and bucking w

June 9 on my way out to work my car started to lose power as I was driving along and acting like it was going to stall so I turned around and started back home. Then it seemed to clear up so I left again and after driving about 10 miles it started again, losing power even with my foot on the gas and then going on but I kept driving trying to get it to the shop. When I was waiting behind traffic I saw some smoke and pulled off the road and called for a tow. They put on a distributor, a coil, repaired the electrical problem (the smoke) and put on a new muffler. When I got the car back it had started stalling at idle and seemed to be running rough but the gas mileage was good and no idiot lights were on so seemed ok. Then the 'service engine soon' light came on and I took it back to the mechanic but other than replacing a $2.00 valve that looked worn they couldn't find anything and said there were no computer codes. So, Friday on my way home it started the losing power thing again but not as bad as the first time and I made it home. The mechanic is on his way to tow it to the shop and test the fuel pump. What do you think? It is a 1993 Cadillac Sedan Deville with 280,000 miles that rides and drives, normally, like a dream and I love the car.