If I get a chance I'll look for the spec on accel enrichment. The system you are working with is MBs first KE and they quickly went to a plus/minus current control.
It sounds to me that you are just responding to lambda control with the 2ma situation. You might try disconnecting the oxygen sensor and see if you get any accel correction. With O2 sensor disconnected you should stay at 8ma except for any correction that is functioning (starting, warm-up, accel).
What is the customer complaint? How is performance?
Bosch Master, ASE Master, L1
33 years MB technician