Really bad MPG since winter hit??

[Moezer]

Hey guys, so since I got the X5 it has been super good to me and my wife other then the 2 back tires going flat at the same time .

But since the cold weather has hit here in Calgary Alberta the x5 has dropped in MPG like a lot!! in the summer it got just around 800 kms now since winter has hit, its not even getting 450 kms to a tank... there is no check engine light or any warnings.

In the summer I put in a cold air intake, its still on the x5, should I put the stock intake back in to it?

Could it be that the intake is sucking way too much cold air and causing the engine to run richer then it should that makes it drink gas like its nothing?

thanks for any help