Same thing happened to my '94 S500. It started to run very rough and the engine 'shook'. I raced the engine and continued to drive. After a few minutes, it slowly went away. I did not shut the engine off.
It 'felt' like it was a plugged injector because it slowly got better after a few minutes. It started immediately, with no warning. It was so rough that you had to keep the accelerator depressed to keep the engine speed up.
Mostly likely, it must have been a bit of 'crud' that partially plugged one of the injectors. It certainly was fuel related.
The only thing that I did that day, was to dismantle the vacuum lines, changeover switches to the AIR and EGR valves. That may have had something to do with it. Maybe dislodged some gunk?
It's only happened once. Very difficult to fix this tpye of problem. Good luck
Regards . . . . JimF
'94 S500 Cpe
Visit my Mercedes Web Page