Cat 312C throttle control knob set-up?

Hi all, need some help from the Cat experts here, have a costumer with a throttle problem, the first 3 settings do knowing, and in no.4 setting it pulls the engine down slightly! I havnt been out to the machine yet, was just wondering if there is any test or set ups to do, or if this needs a laptop to set it up etc! Any help would be great, just want some info before i go out to this machine! will post more info when i get some! Thanks Aiden