I did the same conversion to '91 300GE long, automatic transmission.

There is one problem, engine will stop if i will stop the car(taffic light or to make turn). :-( It is so called "ram air effect".

Matthias, do you have automatic transmission?
Does engine have difficulties if accelerator released and foot on brake pedal, car almost stopped?
Is the air intake modified somehow?

My gas system installer removed big rubber hose from filter to fender, it helped a little.

Danke schön!
Margus