After encountering icing conditions in flight and experiencing problems maintaining altitudes and headings, the pilot elected to divert from his planned destination of Dayton, OH to Knoxville, TN. While on final approach after descending 1300 ft below minimum procedure turn altitude followed by being told the aircraft was well above the glideslope, ATC instructed the pilot to maintain 3000 ft. Shortly thereafter, ATC reported the Mode C indicated 1900. The pilot responded with 'engine quit'. The aircraft crashed in a pasture about 1 mile from the airport. The investigation revealed that the aircraft was not equipped to operate in icing conditions. The evidence indicated that the flaps and landing gear were extended. Approximately 40 lbs of cocaine were found onboard the aircraft. The tox report for the pilot disclosed .05 mg/L benzoylecgonite (cocaine metabolite) in his blood. The pilot had received a weather briefing which included a freezing level at 7000 ft and filed a flight plan requesting a cruising altitude of 14000 ft.