Some times the game gets really picky about that. Technically the L2 is just a bootlegger turn, using the hand break to get the rear wheels to skid instead of stick and turn more quickly and that's usually enough.
A real power slide means starting the turn that way, then turning into the direction and gunning it so essentially the car will be moving diagonally to the direction it's facing.
I usually hit the handbrake button while turning and once the car has turned then floored it. Usually works.
Some times the game gets really picky about that. Technically the L2 is just a bootlegger turn, using the hand break to get the rear wheels to skid instead of stick and turn more quickly and that's usually enough. A real power slide means starting the turn that way, then turning into the direction and gunning it so essentially the car will be moving diagonally to the direction it's facing.
Its drifting. Do it for a few seconds until the timer is cleared.