i own a 83 f150 great truck(some times) ive put more money into it that i payed for it. its a great truck and its just old. it has about 120000 miles on it. today when i started it, it idle wierd not like normal but lower. then my friend came over and we drove around and then it stalled on us we turned it over and it idle extreamly low and later after we got it home it sat for 5 hours or so i had to run my girlfriend home and it began to smoke BAD i turned it off and it quit. we replaced the spark plugs and its not the fuel filter we checks we have no idea whats wrong any infor of what might be the proble please tell(no smart ass remarks like its because its a ford) oh and its a 4.9l 300 straight 6. please i need help