Polaris Diesel Idle problem - any tech advice?
 

Can anyone give some tech advice re. 2002 Polaris Diesel 455 idle problem:
Idle is erratic, even when engine warm.
Throttle lever return spring (under engine top cover plate) seems too weak and without modification even a new spring is too weak to overcome the other spring located in handlebar asembly. This allows contacts in handlebar unit to close and stop engine.
I have taken one turn off return spring and adjustment is better, engine stop contact does not close, but idle is still not perfect and varies.
All throttle parts and engine generaly is in good order.
I have full Polaris worksop manual and have followed all setting procedures, although very little information is given re. setting of springs and adjustment of engine governor.
Any advice would be appreciated.