Pretty sure MAF is faulty. somebody on the forum recently did this same test. Borrowed MAF from wife's car (had to apollo 13 the thing in there with duct tape) same exact happened. When cold the car uses lookup tables to meter air fuel mix. When warm relies on MAF and O2.

You can look at live reading on MAF or even back probe and measure the voltage for some common sense values to confirm.

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)