Possibly a problem with the o2 sensors but more likely you have fouled/depleted cats. What codes are you getting? Some pre-cat codes can be caused by post-cat sensors or the cat itself, I'm not sure if that has something to do with translation or was done intentionally.

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1988 325is (purchased new) sold
2004 X5 3.0 2005 X3 2.5
2008 X5 3.0 (new to me)