John Deere 660j starts moves but won’t idle up
Not sure if it has a throttle linkage or not but I'd check to see and if so see if a pin or something fell out or there's some binding or dirt preventing movement of the throttle shaft. If it's electronic someone like MG should be able to help.
Welcome to HEF Justin . Do you have a full machine serial number ? Is there an indicator light on near the throttle dial ?