Is there a list somewhere on the BB of all possible causes of poor gas mileage? If not, maybe we could create one here. :)

My mileage went from the mid to upper 20s in mixed driving to the lower 20s. I have a B23F with LH 2.0 and M46 tranny). I have a few theories specific to my case but don't want to rule anything out.

My theories are dragging brakes (one of the rear rotors is warped but the car free-wheels just fine and doesn't pull to one side) and a bad coolant sensor. My air filter may be dirty as it hasn't been changed in a few years. My O2 sensor is new - I had hoped that it was the cause but it doesn't appear to be. Plug and wires are about mid-life; it idles and starts fine. AMM is old; I'll do the Bentley tests when it gets warmer to see if it needs to be replaced.

I thought it may be the winter-grade gasoline but usually my mileage in the winter is mid-20s. I use premium fuel due to knocking issues.

Thanks in advance!
--
Mike F - 1984 244 DL - 317,000 miles
Original engine, transmission, drive train, starter
Undergoing reconstructive surgery with POR-15

1972 142 S - The Yellow Brick - 135,000 miles
All stock except for Weber Carb. B20B engine. M40