what to do next I changed the sparkplug and the ignition coil, still misfires.

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I am getting a "service stabilizer; service traction control" message so I thought a sensor was loose...I checked and couldn't see anything, diagnostics gives a p0306 code. Misfire 6 cylinder...sparkplug totally fouled and caked...still misfire, connect a new ignition coil...still misfires...what to do next?