worsening vapor lock - going to vomit now!

I have been fighting with this car for so long now, that I am about to vomit. And I am against that.

I am a pretty good back yard mechanic, but can't figure this out. When the car sits for more than a few seconds, after switching off, it takes several seconds to re-start.

If it sits for about twenty minutes, it takes about twenty seconds to start. Ironically, if it sits overnight or longer, it usually only takes about five seconds to start. If this were any other car, I'd call it "vapor lock."

Usually, after several seconds on the starter it fires on 1 cylinder, then 2,4, and with a rev or two, all is OK...

I have checked most of the mechanical and electronics on the Bosch syste, but I must have missed something. So did my local mechanic. After about three hours on the job, including a fuel pressure test, he handed me back my keys and said that I should go to a Mercedes specialist.

I admit that I felt better that the problem stumped him, too, but still I just want it fixed...

I have checked the accummulator, regulator and individual injectors for leaks, including the cold start injector. All seem good.

Please volley your guesses my way. I'll try anything.

Any chance it's not fuel related, and I am barking up the wrong tree?