Most nitro engines will stall out at idle especially if you got your LSN set too rich it will basically flood itself out. There are a few telltale signs. One is if your engine is sealed and your decent at tuning once your engine is up to temp it will either never hold a tune or it will always stall out. Another way is pull your sleeve and piston out, hold your thumb over the top of the sleeve and push the piston up. If it is really worn you wont feel much of any pressure pushing on your thumb