The builded up heat from the high RPM is still flowing away from the inside of the engine but because the airflow is gone it will concentrate in more heat and is slowly tranfered to the air. When runing idle there is no performance made and so no heat develloped, with that it will slowly cool down. When giving throttle the engine directly cools down but it is not the airflow, it is the rich mixture (at that moment) with the Nitro giving an internal cooling.
I am happy the G-force sensors, it showed 2G. I am still thinking about the fueltemp sensor, I think I have to isolate it much better from the engine and airflow.