My mx3 has been doing this for quite some time now. It never really bothered me until I had to start driving slow and taking it easy on the car through snow. When its in gear it starts bucking and its embarrassing as hell The only code its throwing at me is the vehicle speed sensor malfunction ( po500) but it was doing this way before I had ever had that problem. Truly annoying. When you give the car a lot of gas it bucks and feels like its not giving you anything. Almost like the fuel regulator or something of that sort.