IO540 - it must've been worn out. It would certainly align itself pretty quickly after "power up", and was fine in normal use. But a quick 180 on the ground after "spin up" would "topple" it every time.
We didn't worry too much, because we didn't do a lot of that. We didn't have that particular Arrow for long anyway - the engine blew up over the Solent and the insurance wrote it off.
It's certainly a nice bit of kit, but I think I'd go for a GNS430 before I'd go for one of those.
Don't reckon I'll be in that league again, being a poor retired fella with a part-time job that doesn't pay anyway ;-)