Ok so what causes p0300 is what you siad and if you changed them and still have the issue some how you must gotten water in the gas tank because of humidity or water got in the injectors and you need to add something called heet and make sure you got the right spark plugs because the gap is different in the 2.3 liter engine than the 2.5 liter engine
P0300 code is only these problems and when it's running hot the little bit of water is burning and becoming vapor so the car runs great