I was also thinking F125 as that's the exact same behaviour mine exhibited, right up until you said it did the same last winter but was fine all summer. If it was the switch it should have got worse until it did it in warm weather too, and then even when the engine was warm. Not ruling it out, since its due a change at that age and mileage, but its odd for it to go away rather than get worse.
Where are you? There's probably someone relatively nearby with VCDS who can read the codes for you, then we'll have a much better idea of whats happening
