One other explanation to the sudden change in throttle:

When I was getting my XF chipped, they told me to leave
the driver's side door open with the key in the 'ON'
position for a few minutes. (NOT while the car is
running). IE get in the car, put in the key and turn it
to the on position without starting, leaving the door
open.

If you pop the hood in this state, you can 'hear' the
throttle recalibrating itself.

I'm wondering if some who've suddenly noticed a difference
(after leaving car at airport or servicing) is merely the
result of the automatic throttle adjustment. It would only
make sense, since service will likely have the door open,
etc.

Just a thought.