I'd guess it's throttle actuator related, when problem happens, you can park the car, remove air filter box, then manually sway the throttle linkage from the point where cable is attached, then inspect the movement of the linkage down to throttle plate, there must be something wrong in that part.

The throttle actuator of M119 can be problematic, when it was extremely cold, my 400E almost killed me when actuator stuck at highway speed twice, I did lubricate throttle linkage periodically as recommended.

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99 BMW 540i 6-speed 110K Km
03 SAAB 9-5 wagon 80K Km
92 400E (Sold) 245K km
Still missing the days with the Benz, it kept me busy.