There's no particular reason for a diesel to stall in a turn.
If the engine's idle is too low it will stall when put under load, such
as the power steering pump and, perhaps now, the A/C as well.
However, if the engine's idle speed is normal I'd suspect the engine's
motor mounts - that one is broken and the engine is moving about
stressing the throttle linkage and so the throttle opening.