2003 Protege5 P0300 random misfire

03BLProtege5

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2003 Mazda Protege5
First post on here, but I figure this is the best place to ask.
I have an '03 Protege5 with 236,000km on it, and I've been dealing with a P0300 misfire problem as long as I've had the car.
The misfire is extremely random, and it will be fine for about two months, and then it will misfire for about 5 seconds and come back while it's idling and warming up. Eventually it will start doing it while you're driving. The car will shutter, the light will come on, and power will back after about five seconds.
I have replaced both coils and coil boots, the plugs and wires, both oxygen sensors, the intake boot is replaced with a cold air intake, and the injectors have been tested and cleaned, the MAF, and the EGR has been bypassed, and I haven't found any vacuum leaks. I had another Protege that had a bad EGR valve, and bypassing the EGR the same way I did on this car fixed it, but it hasn't fixed anything with this car.
I also replaced the main cat with a Magnaflow because the original cat was punched out, and the precat is gone because the car has headers now.
Does anybody know what else it could be? I've been dealing with this for seven months. I'm thinking it's the idle air control or VCTS.
 
try cleaning your iac and throttle body up really good. also try unplugging the iac while its idling to see if it kills the car if so its good if not its bad or stuck open. this is a tough one as you have mods i am not 100% familiar with on this car
 
How did you bypass the egr?

Also, which CAI did you install? Make sure it hasn't made a hole from rubbing against the brake master cylinder.
 
I cut the EGR tube and plugged the hole on the header. On the other end of the tube, I bought a piece of hose over it and plugged it with a bolt. It sets an engine light, but it doesn't affect anything and I've done it on two Proteges and it's worked like a charm both times.

And I don't know what the intake is, but there's no holes worn in it by the master cylinder yet, so it's not that. I already dealt with that problem as well on another Protege.
 
I'm going to try cleaning the IAC, but it's hard to work up the motivation when I don't have a garage and it's consistently -35 Celsius out right now
 
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