I got the P0300 error after 3 weeks of changing the coil packs, yet again. At the same time, I was dealing with a bad clutch (thanks to Spec Clutch's poorly designed aluminum flywheel) I was forced to run the car with a very slow aceleration, at around 5K RPM, I felt the car studder and all of the sudden "SERVICE ENGINE SOON", you guessed it, P0300. This time, I changed the "Exhaust Gas Recirculating Valve". It turns out that CO built up jamming the valve and leaving it open at all times. This made a dramatic change during decel (while engage) as well, as a clear sounding exhaust.

Good luck to those with this problem. Hope this helps.