Check Engine Light on Code PO113 IAT Sensor. Where is this sensor located? And is it available from on line sources or is it only available from the dealer?

I read the posts on the PNP switch. I have a code reader for OBDII and there is no code in my computer. The light does not stay on all the time it comes and goes, and I don't think when it does come on that the car is stuck in third gear, most of the time when it comes on we're on the freeway and th...