ive got an 06 magnum 2.7 35,000 miles that will miss sometimes at a low rpm but will smooth out at a higher rpm.but it does not miss all the time.it is also showing a p.0.300 multiple misfire code.i have checked one of the plugs and it doesnt look bad.ive heard about some of these cars that would carbon up the valves and do this,anybody got any ideas. thanx