If the difference is really noticeable then I would say, I'm a little stumped.
I know that on a crisp, cold, dry day, sub 7/8 degrees, then my GTI feels as though as it has slightly more get up and go, than it does on a 16/17 degree day like we had yesterday. I guess it's all down to how much cold air you can force into the car to make it breathe more healthily.
I know that if I've ever had a smoke :embarassed: then I can often find things wrong with my car, that miraculously disappear the next time I'm sober lol