The idle control valve doesn't really affect mixture. The DME knows how fast the engine should be running according to other inputs such as the MAF and accelerator pedal so if that doesn't make sense it might set a code. Setting a code doesn't mean it lights the CEL. I wouldn't go with the URO IAC valve more because it might not work properly right off the bat and add to the confusion, not so much about how long it might last. We had someone here have trouble with exactly that a while back and I think we went through some of that in your other thread. What have you done since you left off from the other thread??

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