MPG after light "tune-up"?
 

Hello all. I recently posted about my afternoon of changing spark plugs and while I had the air box off, I decided to clean the dirty throttle body. I had also noticed, to my embarrassment, that my air filter was pretty dirty, so replaced that.
So, new plugs, air filter and a sparkling clean throttle body, along with new gasket.
Car runs fine and idles smoothly. No CEL, no indication of anything wrong.
So my question is, the computer reset because I unplugged battery during throttle body removal. So my MPG average was a measley 18 after driving around town for a few minutes after "tune-up". Understandable considering stop and go town driving. But after driving for two weeks, mostly highway, I cannot break 27 mpg average.
I do have sort of a lead foot. I drive 45 minutes one way to work, 45 minutes home every day, 4 days per week. Its two lane road and I pass a lot of semi trucks.
Last year, I drove as miserly as possible for around a month and had my MPG average up to 32!
So my question is, why am I not breaking past 27 mpg average AFTER my tune-up work? Just prior to the tune-up, I was averaging around 27.6 and 28 with the same driving habits. Will it just take the computer a little longer get better? Like I said, it's been two weeks since I've done this work.
Thanks gentlemen!

Give it time, the computer is analyzing!

Reset the average mpg again before your drive to work at the beginning of the work week.

What spark plugs?
I have found that the average MPG declines the more I worry about it.
Remember; the average starts new every time you reset it and it includes idling getting zero MPG. So, if you didn't reset it since you did your "tuneup" All of that idling while fiddling with stuff counts.
The only thing you can do for a tuneup is new plugs (ACDelco 41-103) every 100,000 miles. Schedule in Owner Manual. The correct plugs have been known to last 200-300 thousand miles.

I did install the AC Delco spark plugs.

Awesome, enjoy the drive! Be patient

I was today years old when I realized I could reset the average MPG from the steering controls.
😂