when i start it up it feels like its gonna die out but the rpms fall just below 500 then go back up to 700 ,it shakes really bad ,the vacuum gauge jumps up and down,then when i drive it it has no power at all,i havent really driven it much lately,but when i used to drive it , it would drive fine when it would drive for about 2 miles or so.thanks for any help you can give.