I saw a major improvement in MPG when it started coming up on 1000 miles. My advice would be: 1)run the octane the car is tuned for; 2) set the tire pressure to what it calls for; 3) Eliminate the possibility it isn't running right (is it idling ok? Pinging? Detonation? etc) 4) Don't alter your driving habits/style 5)check the MPG again around 1000 miles.