I'd bet money your air mass sensor is bad.Very common.The best way is to test via actual values with HHT or SDS (MB dealer scan tools).
I can't promise you anything,but from experience,put one on.
It is the large sensor attached to the air cleaner box between box and tube going to the intake.
MB part # 000 094 05 48
Mercedes Benz Master Tech
ASE Master Technician
Owner of "Behind the Star Inc."