did your tuner try to make your idle less lopey since you are cammed?

i had the same issue with my cammed VIII, timing was adjusted to smoothen out the lope and it had 300. the car was flashed back to stock and 300 went away.

 

milos definately right. the P0300 code is from the tune, not from the coils. i had my car tuned from turbo trix a couple years back and within a mile of leaving the dyno i threw a p0300. it stayed on for about a year until i started tuning it myself. now i never get the code (same coils, same plugs). turbo trix had adjusted the timing at idle, and thats where i would always throw the code. while idling or cruising on the highway.

 

Well, I would not go so far as to say it is always from the tune. I have tried in vain for almost a year to get rid of the 0300 on my VIII. Stock idle timing, advanced idle timing, stock cam gear settings, advanced cam gear setting, retarted cam gear setting, every variation you can think of to no avail. In my case I think it may be related to the belt tensioner or the crank sensor itself, won't find out for sure till I replace the belt, tensioner, and sensor.

 

your right, its not always the problem... my mistake, misworded that. but it certainly is a problem, as i have fixed a couple cars that regularly throw the p0300 and it was from tunes that fiddled with the timing at idle load cells.

 

Agreed

Back to the O.P.'s thread, what all changed between no P0300's and the P0300's. If you can narrow down the changes that took place between not getting it and getting it, it may be much easier to diagnose. In my case, I cannot narrow it down enough (i had stopped pulling codes cause I was getting constand cat efficiency codes due to my test pipe) and installed cams cam gears transfer case twin disk etc etc before I started pulling codes again... thats when I found the dreaded P0300.

I can't count how many cars we see that really missfire on the dyno when we turn up the boost, but that is always related to the plug's being gapped too wide. In those cases we rairly see a p0300.

If the only thing that changed was the tune, then certainly persue KevinD's advice.