Put it in to diagnostic mode and read the codes if any.
Main suspects are air/water/fuel temp sensors or the thermo wax, could just be damp, stuck, out of adjustment or one of them has packed in. Sounds to me like the ECU thinks the engine is cold when at idle because one of the sensors is telling it the engine is cold when it's not you just got to find out which one/s, it could be other things but start here first.