I have an 03 EVO, mods in my sig.
my first tune ( 5yrs ago) was a mail in buschur tune on stock turbo ( with bolt ons) I got the po300 code every once and a while.

2nd tune (3yrs ago) was by mid atlantic motorsports, in gaithersburg MD
with new turbo. they said the got rid of the po300 problem.
i still got the code eeeeeevery once in a while...probably a true reading though.

recently, for the past 2 months i cant get rid of it. i tired new plugs, smaller gaps, wider gaps, driving WOT, drivin not WOT ( like a normal human) tried new wires, checked all vac lines, check for boost leaks, Nothing. i have a scanner and i can clear it. But it will come back with in 10 mins of driving, every time. Which is new to me. The car is driving smooth as can be too.

The only thing new to the car since the last tune, is the drive train, shep tranny and t-case and twin disk clutch.

I dunno what do you guys think? try coil packs? go to a tuner? or something else. its driving me nuts.

 

visit the ecuflash forums...there are ways of just disabling the code

 

It's like a phantom code. It tends to come and go as it pleases. When I bought my car, it was throwing that code but when I connected it to an autozone scanner, it made it disappear. I haven't had an issue with a CEL since (4 months).

 

i know about the phantom codes and it coming and going. ive owned my car for over 5 years, this is more then a coming and going phantom code.

I clear it, and it comes back no matter how i drive instantly. been doing this for 2 months.

 

I have been having it ever since i put my cams in... but when the weather warmed up the code went away... it could be related to the weather.

 

i guess when mid atlantic tuned it, they didnt get rid of it. and i guess it could be weather related.

 

I have the anti-fouler trick attached to my rear O2 sensor and most of the time the po300 code would not show up. If the weather temps change, like recently when it went from sub-freezing to mid 40's-50's, the code popped up. It's weird but at least it's not a constant thing.

I do want to do the ecuflash thing to disable it permanently and maybe just take out the antifoulers, but gotta read up more on it. But from what I read, it seems like an easy rom update.

 

i have a fouler too, well its kina warming up. i havent driven it in a few days. let me clear it and see what happens