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izanti -
Here is my take on the IAT-resistor-only mod :
1 - It "works" for performance WOT conditions because the ECU/PCM goes into open loop mode. Under open-loop mode, the ECU/PCM uses the IAT signal (as one of many input parameters) to determine fuel enrichment. The settings for performance will simulate CAI readings, aka lower input air temps.
2 - I claim it doesn't work under hypermiling driving conditions because the engine stays in closed-loop mode. In this situation, the IAT temperature reading to the ECU/PCM is ignored. As long as you don't stomp the accelerator pedal, it's not a factor.
On my Saturn, I have tested this with the ScanGauge by putting in different resistors and taking MPG readings over very short but multiple A-B-A test runs. The higher the "temperature spoof", the higher the MPG reading from the ScanGauge. However, the engine maintained exactly the same driveability.
CarloSW2
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