IAT FMIC

[chad99]

Do you turbo experts know why my IATs are always higher when I am in vacuum and always lower while in boost even at the same MPH?

I installed a ebay intercooler (bought it while drinking, car doesn't need it, its stock, I just like saying FMIC) and I don't understand why the IAT sensor now reads lower temps while in boost vs vacuum.
Not just a little difference, its close to 20 deg higher when in vacuum at same MPH as while in boost.
I don't recall this happening with the stock side mount

Other than that the FMIC is doing its job, repeated long steep hills no longer cause the IAT to increase and when its a +100 on a sunny day the IATs are only anywhere from 6 to 11 deg higher than outside, but only while in boost.

I don't know if it matters, but while I was installing the FMIC I found the stupid diode mod from PO plugged in, unplugged it and used it as a door stop.

[old guy]

When you are in boost you are measuring the temperature of the cooled air flowing through the intake manifold. When you are in vacuum the air flow stops and you are measuring the stagnant air as it gets heated up from the hot intake manifold. My TyrolSport SMIC does the same thing.

[Seerlah]

I use an in cabin IAT sensor for digital gauge. Sensor for gauge is plumbed into cold charge pipe. It is here that you really see the intake temps, and learn about real heat soak. How things like a throttle blip in traffic can bring that heat soak temp down 10-15 degrees at times, depending on factors.

ECM IAT has to do with fueling calculations, with other variables like coolant temp, etc. If in positive pressure the ecm sees too high of an iat, it will pull ignition timing. This is why many upgrade to a more efficient intercooler.

[chad99]

Thanks guys that makes sense, I forgot the IAT was behind the throttle body, and I just figured the was no way the new IC was that much better at quickly cooling off air going to the engine than the stock IC, because I swear the stock IC would ALWAYS show higher IAT sensor readings when in boost and lower readings when out of boost.