Nah, assuming the car is in working order with no anomalies the driving cycle, that is the type of driving dictates the fuel economy you get in the moment with no lasting effects.
Highway efficiency > stop and go/city efficiency > wide open throttle
At least, when it comes to your wallet (as pure physics/engineering efficiency favors WOT) combustion engines like steady state.
You're telling us that you're seeing +1 mpg. Is that on your average that you have never reset over 14k miles? Is that on this tank of fuel? Is this on the tank of fuel afterwards? Is this the average of three tanks of fuel?
That statement is open to interpretation so you'll get lots of diagnoses (doctor my stomach hurts, it's either the leftovers or cancer).
By the next tank of fuel you'll be back to normal.
http://www.ft86club.com/forums/showt...18#post2071818