I had the same thing on a 1995 E320 coupe today. On that vehicle you disconnect the line from the egr valve to the manifold and then open the throttle all the way and clean the end of the tube where it enters the manifold, that's where the carbon is deposited which cause the code. Then blow it out with compressed air from the other end.

You need to make a tool to get into the tube not sure if it's the same on an M103 engine.