1996 Geo Prizm problems with car

Engine Mechanical problem
1996 Geo Prizm 4 cyl Front Wheel Drive Automatic

I have a 1996 geo prizm lsi, I just bought it over a month ago. I took it to auto zone and it came as a misfire in the number 3 cylindor. I replace the sparks and it still sounds like a misfire in it. I have checked the injectors and they are good. I used some fuel injector cleaner on twice and recently it has started to stallin when I come to a complete stop. I have checked for leaks and there is none. Someone told me that the emission will cause the problem.