Surges are normally on one engine only, when both engines are fighting each other we call it oscilaton. 212/412 have a long history of this. The engines air systems are linked between engines at the TCU. Lots of things can cause an oscilation and can be a major pain to work out. I can't recall having engine oscilations on the ground, they usually happen at higher torque/N1 settings.
Also, I've never seen a helicopter that is geared for one engine to drive more than the other.