I've noticed recently that my car has had a substantial drop in MPG. 2 months ago I was getting about 28 on the highway, and now I won't crack 24 without even applying the brakes at all. It's not a huge deal to me but it's making me wonder if something's going on with the O2 sensors or something else.. or can this kind of drop be entirely attributed to winter blend gas?
78K miles, new air filter this year, intake valves were cleaned last year. I've also noticed substantially more soot coming out the back than seems normal. Shell V-Power gas.