MPG drop

Colder denser air is a better air charge in the cylinder and therefore can have a greater quantity of fuel to combust completely as opposed to warmer air even when it has been compressed by the turbo then cooled by intercooler it is still less of an air charge when it is watm out than when it is cold. The engine compensates for this by doing the above but way we notice is slight reduction in economy. Its opposite of heat soak in the summer when the air charge isnt sufficently cooled by IC and so you can suffer a loss of performance with high ambient temperatures.