I have followed this subject closely as my M103 is exactly the same and it is a common complaint.

A little bit of throttle when starting works every time. This is even what the Owner's Manual suggests for a warm engine.

I have checked all the associated fuel system parts and recently replaced the accumulator. Nothing has changed the warm start condition however I have greatly improved the response and feel by adjustment of the EHA and by having the engine in excellent tune.

IMHO it is unquestionably to do with old injectors. They don't last forever and 100k miles is the suggested life. They have done a good job already for 15+ years!! One or two leaking-down a drop or two creates the richness that causes the start-and-die. This explains the instant resart or the success of the use of throttle (more air).

It is further explained by the fact that the engine actually continues to heat up after shut-down when the cooling system is not working. This additional heat puts additional strain on the tired injector.

The benefit is that they are not teribly expensive for an M103 and can be changed DIY.

It is the only thing that makes sense although I have not changed mine as yet.

89 300CE
153k kms