Car is running really rough misfiring "popping" out exhaust on idle (similar to leads arcing) motor badly shuddering under acceleration then runs fine then coughs and splutters, then engine light flashes, engine light stays on, turns off , car runs ok, then starts playing up again, ok so far a service had all coils replaced and new spark plugs .default code said cylinder 3 misfire .............help please , 2012 95,000km .......