The box with the three fuses on it is the K40 relay - I'm new to the W210 world and I'm still learning the new web-based ETM diagrams but it appears the K40 relay is responsible for providing power to run the IFI (fuel management) functions on your car.

If I'm reading the diagram correctly the power for the IDI system is obtained before the 10 amp fuse comes into play so it would appear the K40 relay is providing power and overvoltage protection but the 10 amp fuse is not protecting the IDI system from excessive current draw. Very strange.

I don't know if the K40 relay is your problem but if the relay dropped power to your IDI system I'm pretty sure the car would at least stumble and maybe shut-down totally.