If you wish a comparable airflow reading do it with the key on and engine off. That is the only comparable situation. When running the difference between a good AMM and a bad one in a dynamic situation will be hard to identify.

The real test is the adaptation readings. I'm not sure how good an OBDII scanner will be at adaptation numbers as OBDII gives long and short term but MB has three. The important numbers are not what OBDII calls short term, they are CTP (closed throttle position - idle) and part load. Both of these would be long term fuel trim by OBDII standards. I'm not sure what they look like when combined. Long term fuel trim would be the best of the OBDII numbers I would say.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician