Sounds like it might be an issue with one or more motors, have you checked them?It just revs up flys a bit then stops. Sometimes it flips to the left and some time revs up hard and climbs uncontrollably. Now just doing a quick jump then stopping as described above.
- 'Flick' each prop with your finger and see if they all turn freely, and spin for the same amount of time.
- Start the motors with a CSC (pull both sticks down and to the inside), then shut it down with left stick all the way straight down. Watch the props closely to see if one stops before the others.
- Since you say it sometimes flips to the left pay special attention to the two motors on that side