95 280c misfire when hot

WE HAVE A 1995 280C WITH 6200 MILES. WE ARE THE SECOND OWNER AND KNOW THAT THE CAR WAS NEVER IN AN ACCIDENT OR ANY OTHER TYPE PROBLEMS. ANYWAY ABOUT A MONTH AGO IT RAN ROUGH SOMETIMES IN GEAR AT IDLE. NOW SOMETIMES IT WILL MISS WHILE DRIVING IT WHEN IT WARMS UP. TOOK IT TO A GOOD TECH AND HE SAID THER WAS A MISFIRE IN TWO CYLINDERS WHEN THIS HAPPENS. HE ALSO SAID THAT TWO DIFFERENT COIL PACKS CONTROLLED EACH CYLINDER. ALSO WHEN THIS OCCASSIONALLY HAPPENS YOU CAN MAKE IT RUN ALRIGHT BY TURNING OFF THE CAR. HE SEEMS TO THINK IT MIGHT BE A WIRING HARNESS. I WOULD THINK A WIRING HARNESS WOULD NOT RESET ITSELF. ANYONE WITH A SUGGESTION?

THANKS-STEVE