I assume that after it starts and dies you are able to immediately re-crank and start it??? If so there's nothing wrong with the car, but I suppose it could be called an idiosyncacy.

The problem with this starting condition is that you don't get full cold enrichment, but the engine is not "hot" so there is less than full fuel vaporization and the mixture is too lean to sustain ignition and combustion. BTW this "problem" is not unique to Mercs, but exists to one degree or another on many emission controlled engines. The poorest cold starting is usually at room temperature because this is where the EPA certification tests starts, and many engines are on the ragged edge of leaness. Since about 80 percent of emissions are generated in the first two minutes of this 45 minute certification test, OEs keep cold enrichment to an absolute minimum at near room temperature, and this can affect starting quality in warm weather or when the engine is just marginally "cold" as in this case.

The "fix" is to give it a little throttle just as the engine fires, and it should stabilize and run smoothly within a couple of seconds.

You can check the Lambda duty cycle and set it near the rich limit. This may mitigate the situation, but it would be a lot easier to just modify your operating habits than chase ghosts.

Duke