Entirely boils down to your driving behavior. Has nothing to do with break in, nothing to do with eco mode being on or off, or having to counter things like a different throttle map.
Reasons for poor fuel economy:
#1: You brake too much. This is the single biggest factor regardless of driving conditions. If you want to see an immediate, massive improvement in fuel economy, reduce the need to brake. That means coasting to a stop as early as you practically can, or keeping distance between you and the cars in front of you, so if traffic slows down, you don't need to bleed speed with your brakes.
#2: You spend a ton of time idling. Either in park with the car on, or your driving consists of tons of stop and go. Self explanatory; you're burning fuel without traveling any distance and this will bring your average MPG down.
#3: You don't hold speed when you should and spend a lot of time speeding up and slowing down. Same concept as braking excessively, but even in situations like on a highway cruise, if you're varying your speed and squirting throttle here and there, you'll bring your average down.
#4: You aren't cruising in the proper gear (for manual drivers). On something like the Si, cruising RPM should easily fall into the 1500-1800 range below highway speeds.
#5: You're carrying excessive load in the car. Tons of luggage, materials, chunky passengers, dead bodies, whatever. Drop em off.
Everything else is the small stuff. Leaving the windows down while having the A/C on causing drag and wasting efficiency on powering the A/C. Break-ins. Eco mode. All that stuff accounts for nothing in the grand scheme.
Anybody here getting outlying fuel efficiency is just driving selectively hard or hypermiling. All of our cars should be getting the same efficiency lol. And if someone's commute consists of spending a ton of time going 45-50mph without having to stop, they're going to have an insanely high average MPG versus the guy spending 80% of his commute in LA/NYC stop, or the guy that routinely goes on cross-town highways at 85mph.
