Lots of problems with overvoltage protection relays, but they only affect idle and cold running mainly. It seems you have a real problem. I would check the fuel pressure first. The fuel pressure regulators stick and cause rich running to stalling conditions from over-pressuring the system.
If you have good pressure I would verify closed loop lambda control by watching the current flow through the EHA (electro-hydraulic actuator). This is the sole electronic mechanism for mixture correction. It gets technical from there on. Let me know when your ready to test.
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician