This may sound crazy. My 2000 ML 320 will have the engine codes #1 bank & #2 bank running lean. I live at 3200 feet in the mountains of NC I can drive off the mountain and clear the computer codes (2) and no check engine light as long as I/m off the mountain. As soon as I go home, check engine light comes on with same codes. Have replaced all 4 O2 sensors, air filter, spark plugs, and the Mass Air sensor. No difference. Any ideas? Engine runs normal just check engine light on. Trying to narrow it down and avoid a trip to the dealer if possible.
Thanks in advance.

if the fuel pressure is ok, return the air flow sensor and get one from the dealer. Seriously aftermarket sensors suck.