THE ENGINE FLAMED OUT AFTER ENCOUNTERING FORECASTED ICING. (THE PILOT HAD EARLIER USED ALTERNATE AIR, BUT WAS UNABLE TO MAINTAIN ALTITUDE DUE TO THE POWER LOSS). DURING AIR RESTART, TOT ROSE TO ABOUT 520 DEG, THE ENGINE WOULD NOT ACCELERATE, AND QUICKLY DIED AWAY. A FORCED LANDING WAS MADE IN MOUNTAINOUS TERRAIN. THE INDUCTION SYSTEM HAS NORMAL AND ALTERNATE AIR PATHS. NORMAL PATH HAS TWO RAM AIR SCOOPS DIRECTING AIR TO AN AIR BOX, THEN DOWN TO THE ENG INLET. SELECTION OF ALT AIR PATH DIRECTS ENGINE BLEED AIR TO CLOSE THE RAM AIR SCOOP DOORS, AND OPEN ALT AIR DOOR ON BOTTOM OF COWL. AIR THEN CIRCULATES AROUND ENGINE AND THROUGH A SPRING LOADED DOOR ON REAR OF AIR BOX. ON SITE EXAM FOUND RAM AIR DOORS CLOSED AND COCKPIT LEVER ON ALT AIR. ALT AIR DOOR OPEN AIR LINE WAS FOUND TO HAVE A LOOSE B-NUT FITTING AT THE VALVE. CHECKLIST CALLS FOR ALT AIR DURING AIR START. STC HOLDER COULD NOT PRODUCE ANY ENGINEERING OR FLIGHT TEST DATA TO VALIDATE THAT ENGINE WOULD PRODUCE SUFFICIENT VACUUM TO OPEN AIR BOX SPRING LOADED DOOR DURING AIR START.