We did find the cause of the problem, but I don’t think yours will be the same if your engine is new. It turned out to be due to slight gearbox propshaft spline wear – hard to believe that could be the cause, but since we replaced it the problem has not recurred !
What apparently happens is that when a cylinder fires, the initial pulse “flicks” the prop forward and by the time the next cylinder fires, it has not caught up with the prop & flicks it forward again. This creates a sort of negative flywheel effect that prevents the engine running properly.
We came across one other owner with a 912iS engine that had the same problem & cure. Hope this helps someone !
Mark
