I'm driving an '01 S80 and I thought I'd change out the air filter seeing as I'd never done so in the two years I've had it. I went down to Autozone and got an STP air filter for $20 on sale with my oil so I figured it would be good for the car. I drove around with the new filter for a few weeks and the mileage display on the computer shot down from about 20 mpg to 16.5 in that time. Can't say I was too happy about that so I popped the old one back in and reset the counter and I'm around 19 now. Since STP is out of my picture and just sitting around the garage, what do you guys recommend I do now? Leave the old one in or buy a new one? Which brand?
Thanks






