95 geo prism 1.8L having serious run problems

my check engine light came on and i noticed no difference in driving or idleing so paid no attention to it. About 5 months later a reacurring problem developed. the car would sputter and hesitate when u try to accelerate, the first time it happened i was almost T-boned for the malfunction. now the problem has been going on for 6 months. Dealership pulled code and sent me after a exhaust gauge regulator. $375 later and my run problem was still there. They also cleaned my fuel lines out whic did improve its performance initially, but within a month the problem was back. The car idles when it is still cold just fine, but once it reaches opperating temperature it picks up the hesitation, and if u try to accelerate it sputters and if you keep trying to accelerate it will die, sometimes giving a puff of smoke out of the air box (smells like oily exhaust). my car is not burning oil, i rarely hav to add any oil between changes, and i hav never seen the temperature gauge rise above normal opperating temp. I hav stumped many of the local mechanics, they are willing to throw parts at it, but its my money that is buying the parts… I have replaced my spark wires and plugs and cap recently, i also put a fuel filter on it. help please