1991 Other Mercedes Benz Models engine cutting out

My 300e merc is causing the following.
Everyday drive no problem.
If standing without driving for more than 2 days it starts without any problem and after 10minutes of driving it loosing power and than stops. Will not start. After 50minutes of cooling down it starts and than one can drive without any further problem.

Car has new fuel pumps, new fuel and air filter. Fuel relay is not a problem has been changed.
Spar plugs new, leads in good condition, coil has been replaced.
Car is well looked after and regularly has been serviced.
No mechanic even mercedes benz has any idea what is causing.

Please help!