A while ago I installed a temperature sensor in the cold side Revo throttle charge pipe where a water/methanol jet is able to attach. This was done to compare the temperature of the charge air shortly after exiting the intercooler and once inside the intake manifold as reported by the GTI IAT sensor.
When comparing the temperature reading at each location the results were very surprising.
The chart below shows a comparison of the outside air temperature (OAT), air temperature leaving the intercooler (IC_Out), and the temperature reported by the GTI intake air temperature sensor (IAT), while operating out of boost and then into boost.
The most notable result is that the air temperature reported by the IAT sensor while at cruise is 18 degrees higher than the temperature in the throttle charge pipe.
Once entering boost the IAT sensor reports a temperature that slowly starts to approach the temperature in the charge pipe. Even by the end of the boost event the IAT reading is 4 degrees above the temperature in the charge pipe.
Looking at the same data plotted against RPM for only the boost event it is clear that the IAT sensor is slow to report an accurate temperature. Once the engine RPM passes 5000 the IAT closes to within 4 degrees of the charge pipe air temperature.
These results have significant implications for evaluations that rely upon the IAT sensor, common when describing intercooler performance.
One condition often reported is IAT while cruising. As the upper chart shows, this number has no value in describing the temperature exiting the intercooler.
Another intercooler characteristic is how quickly it cools the charge air when entering boost. As the second chart shows, this too is meaningless if being measured by the GTI IAT sensor.
When using the reading from the GTI intake air temperature sensor there is a very small operating condition where the sensor reports accurate temperature values.