My 1990 24 valve 300 CE has this problem:

With no prior starting or running problems, it suddenly decided not to
start today. It fired up as usual for only a second or two, then died.

The fuel pumps prime up, dash lights come on and the car cranks strong
but it will not start. All fuses are intact, as far as I can tell. Since
my car uses the MAS triple relay, and the fuel pumps pressurize on
ignition, I don't think it or they are the problem. Also the
accumulator, pumps and filter were replaced with factory new units
several months ago. I even checked the fuses on the over-voltage
protection relay, and they are intact. As I mentioned, this situation
occurred suddenly. I've owned the car a long time, and it has been
running well.

One thing, however, is that it occasionally dies when coasting (no gas
applied), as when getting off the freeway or coming to a long stop. On
these occasions the car will occasionally die suddenly, then upon
turning the key and starting, will fire up again immediately. No one has
been able to diagnose this, but it has never interfered with starting or
running. (The idle speed control valve, ignition wires, plugs cap and
rotor are fairly new as well.)

It was suggested I test the ignition to see if there is spark, but I'm
not sure how to do that yet. I know it involves a 12 v. lamp and some
leads. But if anyone has an idea of what else to check, I'd appreciate
it. The various ignition modules are quite expensive, and most such
items cannot be returned once purchased. Yes, I can have the car towed
to the Mercedes dealer or and independent garage, but I was hoping to at
least do what I can first.

Thanks for any advice.

C.A.