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I've had some strange readings as well.
I started out with figures in the area of outside temps. Upon cold startup, the outside temp. After going for a while, it's higher by 5 or so, due to the heat soak in the engine compartment.
Once it's gotten hot, the figure can vary by up to 10 over the course of a minute or two. I think that low flow (TPS) lead to higher temps. The incoming air is absorbing less heat from the intake path. Vehicle speed also has an effect==higher speed is more turbulent air in the engine compartment (has negative effect on IAT) and more air passing through intake tract, also negative. However a car going faster can cause increased underhood temps--so positive influence. Also, cruising at high speed can involve small TPSs so another positive influence.
Start after a heat soak and the IAT is way high like 120 or even 170.
For a few weeks I was getting IATs consistently 120 over ambient/actual. Then it went away and seems accurate again.
I will admit that I popped the sensor out a few times to do TB cleaning, etc, and messed with the wiring harness and cleaned the sensor itself with some MAF air sensor cleaner. I gave up after that, and after like a week of doing nothing, the readings all of a sudden were in the expected range (outside temp and up a few tens of degrees)
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