Hi, this car runs well all day, but starting in the morning the odd time will hold rpm at 1500rpm until he turns it off back on and all is good.

No fault codes, he has replaced throttle body & throttle pedal.
i was thinking temp sender so called out at 8am before it was started to check temp was reading, 0c same at my cars outside temp started the car and could see temp readings increase. It has been smoked tested no leaks.

It has done 122514 miles. Any help?