1995 Saturn SL2 rough idle

So how does the car run down the road does it miss fire while your driving?Or does it only run rough when at idle?Also what do you mean if you don't hold your foot on the brake while putting it in gear it slam's into gear?You always have your foot on the brake when you put it in gear.

If you don't have any miss fire's and the idle feel's rough in park I would look at the upper motor mount for being torn or collasped if it get's rough when you put it in drive then I would look at the lower transmission mount for being torn or collasped. Real common for both mount's so I would check both of them. Also do you have code's?