Hitachi zx225uslc - throttle issues

I have a hitachi in the shop with a very inconsistent throttle control. The machine came into the shop for an engine replacement. Upon arrival we noticed that we had no throttle control. We dropped a new engine in and all is well that way. When we were ready to fire the machine for the first time we had it start and go right up to full throttle.. We were unable to idle it back, and also unable to shut the machine down with the key. We have no control over the stepper motor from the cab. When the key switch is turned to the off position, the stepper motor destrokes the injection pump, but after a few seconds strokes it back into full fuel. This doesn't happen every time tho. Sometimes it seems to stay at the idle position like I would think it should. When we turn the key on and rotate the dial, the control arm on the motor moves around a bit, but its very irratic / inconsistent. Sometimes it seems to work ok, than other times nothing at all. We have the low idle screw turned all the way out, and the machine still fails to power down with the key. I have checked the resistance of both coils on the stepper motor and have 5.4OHMS on both which seems ok. If I backprobe the connectors to the motor im only seeming 3.5v @ both coils. The computer have supposedly been replaced by another dealer, with no results (cannot verify this). Also the potentiometer within the stepper moto is reading 2.7v @ its idle position.

Does anyone have any helpful tips, Or even better A WIRING SCHEMATIC!!???

Anything will help, thanks

PS : already tired the learning mode procedure

Hitachi zx225uslc - throttle issues