starts when cold but not hot
 

1990 300se fires right up runs great for 15 min or so then dies and wont start till completely cold again.anything?checked fuel pump etc crank sensor all ok

What engine do you have in your 300se is it the M103 ? i think it might be your fuel pump relay this is only for the M103 if you have m104 engine this will noy apply .First remove the FRP relay and on the base of the relay you will see a number by each pin . Get some wire and link 7 and 8 togetherthen put the relay back in place . Try to start yur car. And if it starts and runs without stoping then you fpr is shot .Important that you remove the wire link you have put on the wire 7 and 8 right after .Reason fuel pumps will not turn off, and then fuel will enter the engine none stop,, this will can damage to the engine so do remove it after your check is finished.

Here's a simple test you can try. With a cold engine, use a hair dryer to heat up the ignition module. Get it nice and toasty and see if it starts/runs......

I had a similar issue on my 300SEL. However, before it dies, it would run very rough. Once cooled, it would start again.

I agree with ILUVMILS - However, you can also put an ice pack on the ignition control module if it is hot and has died. If t starts immediately, the control module is the issue. Found a used one with warranty and no more issue!