Where is the IAT sensor on a 2005 saturn ion - 2005 Saturn ION

Your IAT is a sensor located on the left(looking from the front) of your air cleaner box.
If your going to install a mod chip, Throw away the 5 cent mod chip. Its going to make the engine run even more rich that it already does. You'll be bogging down the engine with extra unburnt fuel and loosing performance and shorting the life of your O2 sensor and the cat.
The IAT sensor "mod" works on some cars (ford), but not the Saturn. Sorry to say.

It may feel real good for a few miles, but your computer is going to BURY that thing, richen up that mix until the thing gets all loaded up on unburned fuel and you you toast your catalytic converter ($400.00).
Thank you for using fixya and good luck.