Nothings wrong with your CPU, its just using Intels power saving mode called 'speed step'. When the CPU is idling it goes into a reduced power mode where the multiplier goes down to 12 and CPU speed is down accordingly. When called upon by any activity or program that needs more CPU power it switches back to full speed automatically. This is a useful feature, it keeps your CPU cool and healthy as well as saves power. You can disable it if you want by going into the BIOS and look for the EIST setting (or C1E) and select disable. Better to leave it as is though.