Like I said, there are numerous stories of the mounts being replaced and it didn't matter. Two separate mount installations for me in 30k miles and zero difference.

I just ordered a new ECU with a 900 rpm idle and when I install it I will report back. It would be nice to find the root cause but I think that would probably involve a full effort by the BMW engineering team.

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Mark
2001 3.0 Original Owner, still going
2012 E70 xDrive 35i Pre-Owned -- sold because no one could figure out the transmission problem