HAD BEEN DRIVING ON THE HIGHWAY FOR ABOUT 90 MINUTES/90 MILES WHEN WE WERE COMING TO THE SUMMIT OF STEVENS PASS ON HWY 20 EAST-BOUND. THE CAR SUDDENLY STARTED RUNNING ROUGH SO WE PULLED TO THE SHOULDER JUST IN TIME FOR THE ENGINE TO STALL AND ALL DASH LIGHTS TO COME ON. TRIED TO RESTART THE ENGINE WHEN A PUFF OF SMOKE ERUPTED FROM THE ENGINE COMPARTMENT AND A BYSTANDER ALERTED US TO VISIBLE FLAMES. THANKFULLY, A PASSER BY HAD AN EXTINGUISHER AND WAS ABLE TO PUT OUT THE FIRE ALMOST IMMEDIATELY. *TR