Hi everyone. Last winter, I had a leaky water pump on our '06 300 Limited AWD w/ 120,000. So I replaced the pump, timing belt and tensioner, put it back together and leak stopped, but it develped a new issue: a rough idle and the CEL (code P0300). Since the car still had OEM plugs in it, I pulled the plenom and installed a set of Champion RC12PEC5 plugs. While the plenum was removed, I decided to replace the EGR valve. Put it all back together, cleared the code and thought I had it whipped. It wasn't long before the light came back on and if the car idled more than a minute or so, the CEL would blink. Someone mentioned that these engines run best on OEM plugs, so today I installed a set of NGK ZFR5LP's, along with a new coil pack set. Once again, I cleared the code, started the car and as it warmed up, it still had a rough idle and the "lightening bolt" light came on. I drove it around and it went into limp mode, so I pulled over, shut it off and started it again. Frustrated, I took it out on the highway and ran the tach to 5k and 80 mph, came home with no lights and a smooth idle. Can anyone shed light on this problem? We just bought a '16 SRT Charger and we're planning on selling the 300, but I don't want someone to buy the car and have the CEL come back on.