on my MB E320 BlueTec the check engine light came on and the car does no longer accelerate, stays in "limping mode" What can this be, why?

Engine management problem have it scanned for DTC codes, Limp mode allows it to get off the road or to a service service center, while keeping the engine RPM low.. This can be something very simple to service.

For me it was a crankshaft position sensor. You can get a good one on eBay for around $20.00 It's a little bit of a pain to put on the car as it's between the rear of the engine and the firewall. I've done it on my mercedes and my Audi. Utube video helped. It probably saved me $500.00 per car.