I usually have the dial set to the instant MPG reading and was cruising today and checked the lifetime MPG on the car and it was down to 21.4 from 22.5 a few days ago.

I've done nothing differently. Same commute to work and back. I don't notice anything else strange going on with the engine that would lead me to believe there is a bad coil in there.

I kept paying attention to it the rest of the way home and it was climbing and dropping here and there, almost as if the reset button had been hit. I didn't reset it, but is it possible the reset got tripped somehow? I've been seeing DISC codes on the dash from time to time.

 

Tank up recently? Isn't this the time of year they start putting more ethanol in the gas?

Sorry, not hip to DISC codes..