How bout an OVP.
Seems like such a cure all (bg), but I am serious. The idle control system is powered by the OVP relay. Since it isn't working, maybe it isn't turned on. Like the KE systems the diesel idle system is very good at "limp home". Almost like it doesn't exist, except...
There also is a base idle setting that I would have to read about to explain, but it is an external adjustment.
Bosch Master, ASE Master, L1
33 years MB technician