The idle temp really has no bearing on anything as it can vary significantly with the new CPUs that have multiple power planes and CPU vcore and frequency, based on load. Security and other behind the scenes programs running can easily change the idle temp 5-10C. None of the temps below 40C are accurate and the lower the temp the more inaccurate it is. A failing fan usually has a whine to it. Many BIOS or add-on mobo applets show fan speed in addition to CPU temp. With so many variables and the idle temps being inaccurate to start with, it's best to ignore them IMO as max load temps are all that actually matter.
I agree many folks are not aware of the true core temps vs. "CPU" temp which is what most BIOS report. That's why I tried to clarify the situation as it's confusing for many people.
In the top CPU forum thread (sticky) I went into detail as to why the temps below 40C are inaccurate on the FX processors and that AMD engineering has stated that this issue will be corrected in the next iteration of AMD Overdrive. Hopefully the information to correct the issue will be released to other CPU temp applet suppliers such as Core Temp, HWiNFO, etc.
Building a reliable PC involves more than just assembling the parts. You need to be able to configure all of the BIOS settings appropriately. This can be quite involved and frustrating as it can require a lot of trial and error with stress testing. It is however often the only means to get a 100% reliable PC.