Not sure if it will help, but perhaps you can adjust the pressure of the presser foot? I suck at FMQ, but have been watching Leah Day (daystyle designs or the free motion quilting project) and how she adapts the free motion foot to work better. Maybe that would help you also?
Good luck. I know all too well what it's like to have a machine that is not performing up to standards (whether my fault or not!) :lol:
M&M