Well I had several HP 17`s with this issue.

Motherboard : DAY11AMB6E0 rev:E
CPU: i5-4200u

Laptop is cleaned from dust,new thermal paste applied. Although laptop is working fine, cpu temp is around 85-90 C at idle (while nvidia gpu is at 33 C).
Even changed heatsink from good working laptop,but same problem. Core voltage is around 1.713 V.

Any clue what to check,beside changing CPU ?

Можно сравнить сопротивление цпу если есть с чем , и посмотреть осцилографом пульсации питателей цпу , также проц может греть пробитая шина USB или РСI-e или азалия или lan