What factor does NOT contribute to improving a vehicle's gas mileage?

Excessive idling is the factor that does not contribute to improving a vehicle's gas mileage. In fact, idling consumes fuel without the benefit of moving the vehicle. While there are situations where idling may be necessary, such as warming up an engine in extremely cold temperatures, prolonged idling can lead to unnecessary fuel consumption and reduced overall efficiency.

On the other hand, factors like proper tire inflation, weight reduction, and regular maintenance have a positive impact on gas mileage. Properly inflated tires reduce rolling resistance, making it easier for the vehicle to move, thus improving fuel efficiency. Weight reduction decreases the amount of energy needed for acceleration and movement, further enhancing gas mileage. Regular maintenance, such as oil changes and air filter replacements, ensures that the vehicle operates smoothly and efficiently, which can also lead to better fuel economy.