Winter Temps and higher LTFT
 

I've noticed that my LTFT's have increased as the winter months have set in. I assume its due to the fact that initial air intake densities are higher in winter due to cooler temperatures.

In the summer, I would commonly see LTFT's around -5% than I am currently seeing at all throttle positions. When you do the calcs, the initial intake density is around 4.6% higher in the winter (using 75 F as summer average vs 50 F for the winter average). Are you guys seeing something similar?

This would explain my gas mileage dropping from an average of 25.6 mpg in summer months to only 23.2 mpg now as well. Just wondering if I should be concerned since both my mpg and LTFTs have changed recently. I'd assume so since there aren't any changes in performance at all, other than my car feels faster with the cooler temperatures. AFRs still look good, along with fuel pressure and KR.

What is your typical LTFT (at idle) now?
Was the -5% number at idle?

I am trying to get a handle on the different (winter/summer) gasoline formulations in Calif. and whether this has any significant effect on fuel trims.

Gas mileage has gone down for me about 2-3 MPG compared to summer. Some of this though may be attributed to warming up the car a little longer.

colder air = more oxygen content = higher LTFTs.

No. In theory, the LTFT would not be affected.

Keep in mind that the MAF sensor measures air mass.
colder air = higher air density = higher MAF voltage = more fuel = correct A/F ratio (i.e. trim adjustment is not necessary)

My LTFT's haven't changed much since the fall when I calibrated the MAF. They're +/- 3 at most.