Trial and error are one diagnostic technique and the downside risk might be small here and it probably nevers hurts to get a new AMM, but the car should be checked for vacuum leaks and the adaptation numbers should be viewed.

After viewing the numbers I will usually readapt to the base line and drive the car a fixed road test of about 4 miles. I then reread the numbers. If large movement is found and their is no evidence of vacuum leaks I then substitute a known good unit , reset the adaptation again to baseline and do the drive again. If the numbers stay put this time I know I have it right.

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