[eriktherod]

Now that I have my ScanGauge hooked up, I am hoping to at least get some additional information about it. I suspect it is 100% normal and every FRS/BRZ does it (or can do it).

deucethemoose mentioned MAP tuning being suspect and I think that's a good starting point. My Si did similar (though less often but more drastic) after having it tuned via MAP instead of MAF.

It's been rather warm here and I think when the intake air temp (IAT) gets warmer, it starts to do this to compensate for less air being brought in. Unfortunately, I don't think it's going to get cooler here any time soon so maybe the guys out with colder climates can chime in? My typical IAT temps seem to be a good 10-20 degrees warmer than ambient air, and are in the 100-120*F. Guess there's a good bit of heat soak in the intake system. :/

Adding to the theory, being idle typically means you are stationary. That would mean air flow is less and heat soak becomes more of an issue (higher IAT) because lack of cooling via air flow in the engine bay. I would also believe that lack of air flow to the front of the car (being stationary) would also make less air pressure in the intake system. All of these factors I believe lead to the ECU trying to correct fuel trims, thus this little blip.

One interesting idea would be seeing if it does it while coasting in neutral (perhaps at various speeds like 10-20-30mph). In theory, keeping it in neutral should avoid deceleration fuel cutoff (DFCO). Typically when you see the 127 instantaneous MPG, that means your injectors are not spraying at all, so it may be possible to test.