2002 Focus misfiring

I am having a problem with my 02 focus zx3 with 135000 miles on it. It started misfiring about 3 weeks ago after my car would be running for a while and warm up to running temp and misfire. I would hear a pop from the engine so I replaced the fuel filter, plugs, wires, cleaned out my mass air flow sensor, and have been putting lucas fuel injector cleaner in for about 4 tanks now, but the problem is getting worse now it is starting to misfire a lot now not at idle but under accelaeration it pops a few times and when I am going highway speeds and try to accelerate it might pop a couple of times but mostly it does not want to accelerate.I.E. Very veryslow acceleration but I put the car on a computer and nothing is showing up no codes or check engine light or nothing I am in las vegas so I don't know if the hot temp has anything to do with it but if anyone knows anything about this please respond before I have to take it in for repairs which 1 mechanic I took it to so far had no idea what it could be