My daughter has 2001 mazda protege and the check engine light keeps coming on and when we pull the codes it is PO300 which is a random miss fire. We have changed the sprark plugs but the problem presists. The engine has a slightly rough idleand once in awhile when you stop it will die but those are the only symptoms. Does anyone have any idea what else could be causing it to misfire? Would like to know where to look so we don't spend a fortune changing parts that do not fix the problem. Thanks for your help

 

I have a 1999 1.6, and i've got the same problem. At first it was just a rough idle and the car would die when you stopped, but now it has progressed much farther. It won't accelerate even if you floor the gas, and it hesitates at the top of the gears. Its also started backfiring when you shift gears. I've also changed the spark plugs (even tried the pre-gapped ones), cleaned the injectors, changed the MAS and nothing has worked so far. If you happen to find the problem please let me know! I'm desperate! Thanks =)

 

Maybe I'm going out on a limb here. But, have you tried replacing the EGR? The symptoms you're describing sound like something caused by an intermittently sticking valve. I would suggest trying to disconnect the EGR valve(not sure how to do thison your specific car)and seeing if the problem goes away. The EGR valve is notorious forgoing (IMHO)within 50k - 75k miles on the 3rd gen.

Just some extra info... I have a 3rd gen and did this with my car. You just need to disconnect the battery (with the car off of course), then disconnect the harness connecting to the EGR (on the bottom of the throttle body with a black round top). Then reconnect the battery, idle the car for 5 mins, and take it for a drive. The CEL will come on when the drive cycle is done, but you will have plenty of time to test. Disconnecting the EGR should do no harm, especially for the short period you will have it disconnected.

 

We did find the problem and it was that the one of the coil packs was bad when you pull the plugs you could tell that two of them where not firing at all so we replaced both the packs, if you do one you might as well do both,and the wires so far it has been running fine. I hope your problem turns out to be as simple . good luck