There's probably nobody keeping up, but I've been doing some work with this because I picked up a TFT.
The Esplora temp_sensor IC seems sensitive to "V_in".
My test for the TFT was the temp_sensor / thermometer sketch, something meaningful with no extra parts needed. I was using a lab supply set to 5V and then connected it to one of the little step-up converters I mentioned and my temp readings were about 4 degs F lower with it. (Incr. V_in → decr. temp reading). The step-up's O/P is 5.1V The temp_sensor IC runs from 5V directly.
I have, definitely, ohmmed the pins out and the USB 5V pin is 0_ohms to the Tinkerkit 5V pins (and Gnd is Gnd).
It's NOT the temp_sensor IC; it's stable. It's the ADC, its reference is "supply".