My 300c started running rough and the light came on during a recent long road trip. When we finally got it home it spit up code 300 and 305 indicating an problem specifically with cylinder 5. I changed out all 16 plugs but the problem persisted. I just changed the coil on #5 but it still didn't fix it. I'm researching now but any suggestions for a logical remedy/next step would be much appreciated. It's at 130k miles and has been a champ until this. Thanks everyone and Merry Christmas.

 

Welcome to the site.... Sorry to hear about the miss fortune.. Sounds like you have started covering the basics. Good to cover all those first!!! Check the injector make sure that is in working order. Might check for a weak valve spring. I know on our 2012 300C we had to put heads on it at. Luckily we had the extended coverage and Chrysler picked up the repair cost less the deductible. If I remember correctly it cracked the head in the #5 Cylinder for some reason. Hope that is not the case here. Hope you find it just has a bad valve spring. Good luck. Keep us posted.

 

Maybe a bad valve seat ?? Check the valve springs like said !!