Jerky Hyundai 210 LC-3

Hello ,Where I work has a Hyundai 210 LC-3 ,the travel and swing are very jerky unless you idle it down to @1500 rpm or run two functions at the same time. Turning the rheostat does not help. Is there any fix for this or is the nature of the beast?

Jerky Hyundai 210 LC-3