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.

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Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician