1988 Chevy Camaro runs rough,stales at idol,smoke somtimes

I bought this car yesterday, seller said it only neaded som vacum lines fixed. I drove ithome it ran but rough,cut off when clutch was depresed. I repaired two cracked vac. lines set idle high so it wouldnt stale,it helped some. sometimes it doesnt smoke at all, somtimes a lot of white smoke from exhaust,it does have a large hole in the muffler. when driving it hard has plenty of power when driving normal the rpm's jump up and down. could this be my timeing, a sensor or should I just shoot the thing? Thanks for any input. Keith