I was getting around 27-28 mpg all around driving for the longest time, and pretty happy with it. Lately, I noticed just the slightest drop in performance (though I still kept pace w/ my buddy's BMW), and about 24-25 mpg mileage. When you drive about 100 miles a day, that gas can add up, especially with climbing prices! All I did was change the oil (5w30 for REALLY cold weather...) including an oil additive, XR-1 or something like that. I also washed and re-oiled my cone filter. Any ideas? Thanks in advance!

Maybe just a tad too much oil on the filter and some of it has gotten onto your MAF? Just a thought.

I haven't had a chance to check the MAF, but I think I'll just make a list of things to look at, and that will be #1. I'm also thinking check the plugs, wire condition, 02 sensor, etc.

more ideas; winter gas, tire pressure, pcv valve

IIRC, that thin wire in the MAF heats itself when you start engine to clean any contaminant.

 

Why don't you try to reset the ECU and see if that works? You might have changed the ratio of air/TPS position by cleaning the air filter.