Originally Posted by coloradoracerguy

Colder air is more dense. Denser air means more fuel is required to maintain the same a/f ratios. My truck is the same way. The computer is just compensating for what it sees as an increase in airflow....something else to consider as well, do you start and warm your vehicle before you drive it? If so, cold enrichment and warmup burn more fuel as well, causing your average mileage to go down......