1996 Pontiac Sunfire

This is a on going problem I have had it two a few diffreent people and the problem is that the car starts and runs relly rich. I have no codes and a list of parts that I have changed some made run a little better but not fixing the problem. We started with the map sensor, then went two the computer, the coolent temp, timing chain, injectors, all along I have been putting in new plugs 3 or 4 sets they all come out right black. The only way too start the car is to put the pedal to the floor then is starts but runs with a miss. The scaner has been of no help the car can run with it hooked up and all of the reading are in range or close but it will not even show wich cylinder is missing and keep count, it shows cylinder 2, 3 have slite miss but it will not stay on the screen or keep count of the miss. I dont know what else to do but it is starting to get very costly and not shure if I should put more money into it or not. All if the parts that I have replaced where worn but still working, the timing chain was streched out, the injectors had a small drip, map and temp read ok on scaner but tryed in hope that it would fix the problem