I have 100% the same problem except now my car doesn't start at all and it was towed and put in my garage. If you find the answer please let me know at xsohaib@hotmail.com I have thus far changed the fuel check valve, and the fuel filter. I am gonna check the Over voltage protection relay and the Fuel pump relay next. If that does not work then I am gonna go for the fuel accumulator, or fuel injector and eventually if nothing works pay somebody $450 to JUST diagnose the car.
But being a student I am a bit stretched for cash. BTW I have a 420SEL.

Hope this helps
Sohaib