Most PEA Bang For Your Buck

[Nesterenko]

Perhaps I'm overestimating the performance of top tier fuels.

That's debatable but really, who knows. Cheers...

 

[Revving2Redline]

Believe it or not, the ultra thin oil will not help MPG. Often the ring sealing is so much worse, MPG suffers, especially on experienced engines.

Guessing that camshafts are fine, as a mistimed cam will absolutely run poorly, and very likely generate codes (not always though).

If I had to take a stab at it, I'd say your O2 sensors are tired. I'd also note that some engines, for various reasons, really do poorly on fuel with ethanol. I'd try your injector cleaner. And I'd try a full tank of 0 ethanol fuel. While not a 'solid clue', near miraculous results with 0 ethanol fuel does point to lazy O2 sensors.

Use a quality 5W-30 synthetic, change regularly, and consider replacing the two sensors upstream of the cats.

I almost wrote similar stuff that you posted. I want to bring to light the fact that this car is a 2007 so my guess is it was made in 2006 with it being 2025 right now we have a car with barely over 100,000 miles in 20 years. My guess is try to find a 89 octane where the 87 is E10 and the premium is non-ethanol. The 89 will give you somewhere between a 4 and 6% average ethanol content but what I'm really thinking is the big issue is you have a tremendous amount of carbon buildup from a car that really hasn't driven that far. I would invest in the red line for the fuel tank, but also a can of the gum out multi-tune and maybe use a little than 1 oz per quart and add it to the crankcase for a 5 to 10 minute idle before you do an oil change. I'm going to take a wild guess and say that the reason why the mileage is so bad is because I think there's carbon inside and build up.

 

[Davejam]

Perhaps I'm overestimating the performance of top tier fuels.

Top Tier additive designation requires Intake valve deposits (IVD) are less than 50mg whereas the EPA standard is 100mg.
So, while its not zero, it is significant. I would say Top Tier fuel should be sufficient for most folks, but you might want to consider running more of a maintenance dose more frequently.