What is causing a chronic misfire in cylinder 3?

When I picked my car up, the engine light wasn't even on. I still felt some misfiring, but still no light. This was Tuesday night. The engine light popped onyesterday morning, and I have not gotten the code read again. Seeing as how my mechanic said it was still misfiring after the EGR valve cleaning, I assumed the code was just for the cylinder 3 misfire. I will stop by advanced auto tonight and have them check it again for me. A friend of mine suggested it could be a nasty fuel filter, and I asked my mechanic and was told right away that it wasn't, because a fuel filter related misfire would occur in multiple cylinders, not just one. Still havent checked it tho. Driving to work this morning, I drove with a bit of a heavy foot. When departing from a stop sign, as long as I hit the gas a bit hard, it did not misfire much, maybe a little rumble. I noticed as long as I put a little force behind the gas, it does not misfire, even at a lower speed. Traffic is a killer however. It just seems like pushing down on the gas a bit hard gives a burst of air flow or something to possibly something clogged or closed up. Possibly an intake issue? Possibly still an EGR issue? My mechanic flushed out my intake and other parts with Run-Rite. He let it really soak in there to get rid of any carbon built up. If this turns out to be an EGR misfire code, how best to handle that? Replace entire vavlve? Will an EGR misfire still cause the compression issue in that cylinder? If its reads cylinder 3 misfire, what are my other options for the cause? O2 sensors? I was told everything else was good mechaniclly. I know what code to look for if it was catalytic conveyor related. Driving with a misfire will eventually lead to catalytic converter issues, wont it?

I will check code tonight after work and then post. Thanks!

And the verdict is in: P0303 cylinder 3 misfire. Kinda knew that tho. The guy at advanced auto said something to me and I really have the urge to curse out the guys who have been working on my car. He remembered me from the last time I was in there getting scanned (that is so sad). Gave him brief rundown of how many times parts were replaced in the past 3 weeks and he just blurted out "check your coils" I dont know why, but I guess I already thought my guys had done that and thats how they came to the "idea" it was something electrical causing the problems because everything else was mechaniclly sound. Very interesting. How would I know for sure it was the coil pack? I guess by process of elimination is one thing: plugs, wires, cap, and rotor had been replaced about 4 times within the past 3 weeks, fuel injector replaced after it was apparently stuck in the "open freely and just pour fuel everywhere" position. Which is odd because that was never an issue before! Im just mad that I try to get rid of raggedy 2002 plugs and wires and stuff and it has caused more problems. Could this misfire also be something electrical? I just want my baby running nice again. :(

Another quick question - would resetting my ECU do anything, or no because of the drivability issues? Is the engine light coming on because there truely is a problem that is causing a continous misfire in the 3rd cylinder, or is the cylinder misfiring because the engine light keeps coming on ( ie:a short somewhere)

I was kind of concerned about the plugs and wires. After the inital tune up, the first misfire (in 5) was due to a bad wire. It was replaced and ran sweet for about a week. Then cylinder 3 started going bananas and has not stopped. Up until 3 weeks ago, everything was original Mazda parts. Plugs, wires, cap, rotor, all original from 2002 and never one issue. I did not get my old parts back, and now I am regrettng it. Someone else had warned me about crappy aftermarket parts, and if I had my original Mazda plugs and wires, etc, I could test the quality of the replacement parts by throwing the original ones back in and seeing if I still misfire.

So even tho I no longer have an EGR code, that could still be the culprit, but its just not throwing out the code? So if I disconnect it and no misfires, is it safe to assume the whole valve just needs replaced with a brand new shiny one? Now, I have had the valve cleaned. Wouldnt this keep it from getting stuck open due to carbon build up? Cylinder 3 does have a slightly higher compression, 180 vs cylinder 1 & 5 at 150. My mechanic used Run-Rite to decarbonize, so wouldnt this of gotten rid of all that build up and return compression back to normal? What about the cylinder itself? Could the cylinder be bad(i hope not!)Would there be the same "symptoms" if there was a problem with a worn out cylinder or piston rings? I refuse to accept the fact that it could be something needing a new engine. I was told my car was in great condition and mechanicly sound.

One last question right now- how would I know if there was coolant leaking? Smell? Residue somewhere? U guys are great! Thanxxx :)

I will work on the EGR valve this weekend. Disconnecting to see how my car acts.I have been driving my car to work and back, pretty much it because im really paranoid. Am I just killing my cat convert?