Won't help immediately with your idle, but there are modern fuel rail upgrades for the kjet system.
These guys have a kit that you can install in leui of the original CIS one.
https://kjetkillers.pl/pl/p/Zestaw-wtryskowy-piggyback-EFI-Mercedes-V8-m117-/77
Page is in Polish so use a translator.
This guy can rebuild the WUR kit for you
http://www.k-jet.biz/