Rich Rolling..
Even though I have a different make/model car, the concept is still the same. I have a A/F gauge in my NISSAN S13 and I notice that my car runs rich at over 3500 rpms. I was driving back from San Diego last night and I was scoping out my gauge the majority of the way. I've been sceptical about my mileage because its never been better than 17-19mpg (mostly city, little highway). Then I realized that in the city, I mostly drive with the pedal in 2 positions: up or down! There's no inbetween with the way I drive, I love flooring it. Anyway, on the highway its a bit different. I guess when the RPM's are higher the injector cycle duty is obviously higher, therefor the car runs rich. As they say, its better rich than lean.
Anyway, this only happens when I exceed 75 mph, which is usually illegal for most normal drivers. I cant imagine getting "normal" gas mileage when you're flooring your car or doing over 80.. but hey, thats the only time you get a "rush" of adrenaline. =)
- Mike Mamos / ClearCorners.Com / NISSAN S13