It's more important which temperature is at usual or full load. Idle temps should be about 10 -15% higher than ambient temperature. Other than CPU cooler itself, ventilation in the case can also influence CPU temperature. Defective CPU is a very small chance. You should also check voltages GPU works under and CPU cooler fan RPMs.
"Idle" CPU state can also be a variable but that depends what OS is doing at that time you consider as idle. OS could be doing a lot of things in the background even when you don't do anything intentionally.