I live and have worked my whole life at sea level so it this isn't part of my experience. My guess is basically lambda handles it when in closed loop. Those cars required technician centering of the control system and that would be done to suit whatever altitude one sets it at. Later cars centered their base setting through adaptation. KE cars with altitude correction would alter the base setting with altitude from the settings at adjustment (at least from sea level).

As to airflow meters. The one thing I know from training is that technology went from airflow meters to air mass meters to deal with air density differences which suggests to me that airflow meters wouldn't compensate directly for altitude.

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