my experience has been that the vibration (and possibly disturbed airflow) caused so much wild gyration in the vario readings that it seemed pointless to try to determine if I was flying into rising air, so I just climbed first, then shut down the engine and started a thermal search.

Hi Frank,
My ApisM is equipped with a pneumatic toggle switch that disables the rear-fin-mounted Total Energy probe. It is vital that you have this. It completely eliminates the wild vario readings so that you can detect thermals and circle in them with the engine on. This greatly boosts your climb rate and you get to shut off the engine much quicker. When the engine is retracted just flip the switch and you are back to TE mode.