Even here in so cal where its only 45 right now, the engine revs stay up for a minute or so i think it depends on temperature. Id warm up the engine for 2 or 3 minutes and see if this changes the condition. I think its probably normal.
You might also want to clean your throttle body and especially squirt some throttle body cleaner down that iac hole while you do it, because maybe the iac vanes inside are just a little dirty and sticky from the cold. And so maybe they are opening a little too slow until they thaw some from engine heat.
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