i have 06 mini cooper s convertible automatic with 40k miles.
i've been driving local for 10 miles and turned a/c on while driving.
while i was driving in local and slow down the car, suddenly car was bouncing forward even though i was stepping on brake. i even felt like (not exactly) engine also bounced. rpm was unstable as well. when it happened rpm randomly goes up to 6000 and back to normal. is there something wrong with gear box? or misfire? it happened especially when a/c was on.

 

bump

 

has it happened since your original post ?