In near thirty years working on MBs I have seen one cold start valve bad. But, I continuously hear of people with problems with them. It has to be the easiest part to diagnose going. The easiest way is to remove the line and plug it. If it gets no fuel it can't leak. By plugging the source you eliminate both a leaking valve and improper control.
If you are still getting fuel on the plugs you are seriously overfueled. One test would be to pull the fuel pump relay and see if it starts as the fuel clears from the system. If this is the case I would do the base calibration I mentioned above.
Bosch Master, ASE Master, L1
33 years MB technician