I have a 2013 Lexus CT 200h and I've noticed that at times, mostly when driving in sports mode, that the engine will stay at a high RPM even when not accelerating then it will very slowly come down to about 1000 RPM. I live in Vegas, where we usually have daily temperatures about 100 degrees Fahrenheit. I don't know if the heat has something to do with it or what. I do have the Lexus CT Injen CAI installed if that would affect anything? Im curious if anyone else has the same observations.
I have noticed mine doing it on warmer days too. It did it one day last week when the temp was around 80. I was a little concerned at first but then I realized the battery was sorta low so I just assumed it was charging.