Pre Cat O2 sensors replace, still one shows "aging"

[David Shealey]

I have two codes that continue to show up on my 2001 740iL, Off idle mixture control, cyls 1-4, and Pre Cat Oxygen sensor aging, cyls 5-6.

I have replaced both Pre-Cat O2 sensors, but the code keeps coming back. What else can cause this code when the O2 sensor is new?

Also, this cylinder numbering is strange to me, used to the "more normal" numbering of 1-3-5-7 on one side and 2-4-6-8 on the other.

How is the BMW V-8 numbered?

Any "most likely" culprit for the Off Idle mixture control error?

[tbob38]

The right hand bank is 1,2,3,4 and the left is 5,6,7,8. I'm just breaking in on these cars now (have '94 740i), but I would check that something (wire) has not been crossed between the banks.