I did have exactly the same problem if you could search for my earlier post about 2 weeks ago. I used my GMC water blaster(Italian pump) and my car also refused to start the next day. I was shocked as it always started first turn without stepping on the accel. Its a 1994 C180 with 194,000kms. I then stepped on the accel. and kept the starter motor turning and it started after a few tries, but I had to keep on stepping on the accel. or the engine would die. This kept it turning for a few minutes and I stepped harder and released a bit and watched the Rev. counter so it wouldn't go lower than 1000rpm. Eventually it idled at 850rpm which is normal and since then I don't have the hard starting anymore.
No one can say why, but a brainhead said that I must have sprayed directly into the front grille which I may have and this could have shocked the poor car and it had a heart attack or a stroke. Maybe there are some relays or whatever in the frontal area which could have been affected by the high pressure wind and water spray. Anyone have any clues about this???