A huting idle when out of gear sounds to me like an Electronic Throttle issue. Coming from Volvo in the past, I saw that OFTEN- more so then i should have... As well, it could POTENTIALLY be an Air Mass Meter (Or Mass Air Flow Meter as some people refer to it) or the Oxygen Sensors. How is your gas mileage? I would get it to the dealership for review. Is there a check engine or check engine electronics to coincide with the problem???

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