A code P0113 may mean that one or more of the following has happened:
Internally failed IAT sensor
Faulty connection at IAT sensor
Open in IAT ground circuit or signal circuit
Short to voltage in IAT signal circuit or reference circuit
IAT harness and/or wiring routed too close to high-voltage wiring (e.g. alternator, spark plug cables, etc.)
Faulty PCM (less likely but not impossible)
Something tells me that a wire is routed to close to the IAT harness. When I did the big 3 upgrade the light came on sometimes. Once this new alternator went in, the light stays on!
I actually added a ground. I have one coming from the alternator, One from the bottom of the engine, and then two to the frame. All these meet up at the battery. Reason I did 2 grounds to the frame is because the original factory one is screwed up. It looks like its going to break, so I added a second one.