IAT sensor

It should throw a code. I am surprised it did not set a DTC and SES light. If it is unplugged I believe it defaults to something like -40 degrees and the PCM will richen the mixture.

Ranger said:

It should throw a code. I am surprised it did not set a DTC and SES light. If it is unplugged I believe it defaults to something like -40 degrees and the PCM will richen the mixture.

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Ranger, from what I have been able to determine through some experimentation, the PCM does not constantly sample the IAT reading while driving. It acts like it takes occasional readings and multiple failures on those occasional readings has to occur before it sets the code. In the meantime, I'm guessing either it runs on the last known good value from the sensor since the mileage doesn't seem to go down, or the O2, TPS, and MAF sensor readings compensate for the lack of an IAT input on a temporary basis. I could be totally off base with this, but I've wondered the same thing and this is just what I came up with by process of elimination and unscientific experimentation since nobody answered the question when I asked it either... FWIW.

Well, the one thing I know for sure is this, when I first bought my last car ('97 Deville) I checked the air filter and like a dumb shit, I forgot to plug the IAT back in. Got the SES light and since it was still under warranty I took it in. Boy was I embarassed when they told me the IAT was unplugged. With a sheepish look on my face I said "Gee, I wonder what dumb shit did that". Then smiled, thanked them and tucked my tail betweeen my legs. So I am pertty sure it is supposed to set a DTC. You may be right on the other points though.

o2 sensor would compensate for it immediately, or within ~4 seconds in closed loop. Don't know why it wouldn't set a code.