I have the following problem with my mb 190E 1.8 (1992)
when i have driven a few miles and i push down the pedal to shift gears the engine stops when i than let the pedal come up fast again it starts again trough the forward motion of the car
it mostly happens afther a few miles
my mecanic does not know what it can be

Have your mechanic check the idle speed control, sounds like it is not maintaining rpm when cold.

Best Regards,
Jim

it also happens when the engine is warm

Even more likely a problem with idle speed control, as in it is not controlling the idle speed cold or warm.

Have your mechanic start there.

Best Regards,
Jim