Q&A

 Master

Is your 300E a diesel? Sorry, don't know MB too well, but if it is, it might be the glow plug system. If it's not a diesel, check for vacuum leaks, this will do exactly what you describe.

 Master

it could be the coolant temp sensor or the air temp sensor this sensor gives the temp information to the ECU which enables the car to start without any problems

I have the same car, and had the same problem. It was the coil, problem was when
the coil was checked, using the old "jump a spark to something metal test" it appeared
to be, a strong spark. This is deceiving because, the appearance of a strong spark
doesn't mean, that the spark is getting to the plug. Have the output of your coil tested.
At the same time, you might want to have your crank reference sensor checked.

... same car, same problem, solved it with a new coil. Have the out-put of your coil, and
crank reference sensor tested.