I'm not surprised. The stock airbox may be restrictive relative to a CAI but it certainly does a good job of keeping out engine bay air. A good CAI will achieve the same intake temp as the stock airbox but I doubt that it could do much better.

Was your idle temp at the beginning or end of the trip or an average? Where is the intake temp sensor on the X5, is it integrated into the MAF sensor?

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Wake up every day that would be a start.