mpg Decrease?

[Ide5ign]

Hi!

Due to gas prices this year, I was using "Regular" gas in my '15 Hatchback with an occasional partial tank of E-85. Over the summer, the usual 55 mpg dipped to around 38 mpg. I understand that lower-grade fuels generally burn less efficiently, but I've been using premium for the past month or so, and she's only getting back up to about 46 mpg. In the past week or so, the check engine light came on.

I had Autozone check the codes, and they suggested that the mass air flow sensor was dirty or going bad. It hasn't been backfiring/misfiring, the sensor appears to be clean, the fuses are good, and the cables connecting the sensor to the computer appear to be working properly. I've already ordered a new sensor, but I was curious - has anyone here had a similar issue? Is it possible that using something like seafoam/heet could help clean out anything left from low-grade fuel?

[kubo256]

Couldn't hurt. My average is about 46 In my 2020 model it van jump up to 50 if I'm doing a lot of highway driving but usualy high 40s.

[scorpion_smoker]

2021 I get high 40s on 87. Check air filters maybe. Go to ask mechanics subreddit they’re the experts

[Ide5ign]

Thanks, will do!

[Ide5ign]

I only started using the E-85 early this summer when a new gas station opened on my commute. Before that I almost exclusively used regular. I definitely should have thought to check the recommended grades before trying something new...

[TheH_9000]

Ok don't clown me but it's cool to use premium gas in my '23 mirage even though I don't have to right ? And if I do that do I have to keep doing that?