i have an 86 ranger and when i am siting, come to a stop or going along at a low idle it will start bounceing and black smoke will come out. That was cool when i had the dual exaust, it would leav two black spots on the car behind me. But when i put the gas pedal down all the way it will run good and take right off.

 

Sounds like it's running rich. Is it EFI or Carburated?

 

it si an efi 2.9