Here's what I saw: Note that while for the most part the car is just idling at a constant RPM, the idle PWM duty is all over the place! Note also that MAP and MAF are pretty much constant, indicating the load on the engine is not changing. Over the span of the log shown above, the PWM idle duty goes from 18.8 to 33.7 which is just about its whole range! While they're not shown in the image, AFR and EGO correction remain pretty much constant the entire time, so I don't think there's a mixture issue.
The log was taken on a very cold day (about 0 F) and my best guess as to what's going on is heatsoak of the intake manifold which would reduce the density of the air going into the cylinders and require the idle valve to open more to compensate.
Why the MAT reading increases during this time (from about 1.5 degrees F to about 15) is something I can't explain. The MAT sensor is located between the intercooler and TB, and the intercooler is mounted beneath the bumber nowhere near the radiator or any other heat source (on this car the radiator is beside the engine, not in front of it).
I'm just curious if anyone has any thoughts on what could have been happening?
.zip of about the last half of the log attached if it helps. The site wouldn't let me upload the whole thing, even zipped.
