I have a fuel economy question: I have a high mileage 924-S. The engine was rebuilt about 50 K ago. I have gotten a good solid 27 mpg for over 100K. I'm getting about 22 mpg now, and have for a while. The car runs good, idles good, and I see no problems. I did notice that the mpg guage seems to get real erratic at times. Today, on interstate with a steady engine load, the guage seemed to want to swing from 0 to 60. Later is was nice and steady. I think that I read that this guage really just shows the duty cycle of the injectors. If that were the case, wouldn't I see some performance problems when it went from one extreme to the other?

I plan on taking a look at the oxygen sensor. It doesn't have that many miles on it, but they were miles where it was running a little too rich (I think) due to a broken intake valve spring on #1.

The plugs, plug wires, cap rotor, and injectors (rebuilt) have about 5 K on them, and I don't think they are the problem. So what other things should I be looking at?

My buddy, the Porsche trained mechanic gave me the old "You drive a Porsche and worry about miles per gallon?