Have a 1990 firbird formula 5.0 tbi,116000 miles,car starts fine but tach starts to jump like crazy,sputters some,when taking the car for a drive it is fine ,but when i come to a stop it dies on me,start it agian and take off all is good until the next stop,then it dies again,under power it runs fine but when youcome to a stop it acts up and wont run or just stops,i have changed the map sensor,02 sensor,any help would be great,thanks