Hi AlexK -
(I'm not an expert on this stuff by any stretch of the imagination, I am only repeating stuff I have read up on. Please correct me if I am wrong !
! )
I don't think you can get these kicked off ebay, they are there by the hundreds. They're like weeds.
I think the gimmick works, but I can't say what the long term effect on the engine will be. It's just a resistor that replaces your IAT sensor. I went for the gimmick too, just to see what it was. I always go for the cheapest version of a scam, so it "only" cost me about $6 total. It was just a resistor and some instructions. Therefore, I paid somebody $6 for a 25 cent resistor. The fancier ones are packaged in cute little boxes or can snap directory onto the IAT sensor connection (less mickey mouse).
For performance, the resistor is chosen to tell the CPU that the IAT is colder, leading to more fuel being injected (rich fuel/air mixture), aka super cheapo Cold-Air-Intake. For fuel savings, the resistor is chosen to tell the CPU that the IAT is hotter (lean fuel/air mixture). The only "skill" involved here is picking the right resistor for the right car. In both cases, you may be short circuiting your emissions (that's why I never installed mine).
To me the following would be a safer (and more complicated) way to implement the gimmick :
1 - Get a ScanGuage (the mechano-bio-feedback device for any GasSaver).
2 - Install a potentionmeter setup in place of the IAT sensor (I don't know how to do this, you need an electrical GasSaver guru for this). The potentiometer will allow you to select whatever IAT temperature you want the car's CPU to "see". In the car, it will just be a dial that you spin like a volume control to pick whatever temperature you want.
3 - Install a separate "IAT" sensor (let's call it IAT2 for this discussion) for yourself at the same location as the car's IAT sensor. This way, you can know what the real Input Air Temperature is at any time.
With this setup you can know the following :
A - The ScanGauge will tell you what the potentiometer is telling the CPU.
B - The IAT2 will tell you what the real outside air temperature is.
With this setup you can decide whether or not to emulate the IAT2 outside air temperature or to "shadow" it. That is, you can be adjusting the potentiometer to a temperature that is maybe 40 degrees F hotter than the IAT2 reading. Conversely, if you don't like how the car is driving, you can emulate the outside air temperature. I think that the rate of change of the outside air isn't too great that you can't fiddle with it and still drive safely.
...
I think that the *real* thing to do is piggy-back the potentiometer with the real IAT sensor in order to bias the IAT sensor into always reporting +X degrees F, but I don't know how to do that.
CarloSW2