The engine actually does not have to be warm to make the idle mixture adjustment. However warming the engine is part of the procedure for checking the output of the mass sensor. I would not worry about the mass sensor too much because these AFMs rarely fail. You can also clean the hotwire with a quick blast of electronics cleaner.
More good information from the forum on DiscoWeb …… https://discoweb.org/index.php?threads/tps-and-maf-adjustment.58832/
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