I have a zx225uslc-3 that when you let of controls it abruptly stops and shakes machine badly. Pilot pressure and main pump pressure are with in spec. Pump regulators are working as they should. It does it the worst on the arm. It gets worse when oil is warmed up
that is an interesting fault. what pressures did you check and what were the values. Does the machine do this for all functions including the travel system. Do the functions seem very fast in operation when trying to do small movements. I would check how the output signals to the control valve respond vs the the pumps flow control signals as it leads into the starting and abrupt stopping of the function. Is sounds like either the pilot control signals have a high starting rate of control or the pumps flow output is too high.
I might have found the problem. The arm flow rate control valve seat has a groove in it.
nice one. let us know if that fixed the problem.