It will most likely be an application you have running Bikkit. If you click on the CPU heading under Processes, you can order your running tasks by which application is taking up your CPU. You will most likely see the application that is using the CPU. You'll find that just moving your cursor around your screen will use up around 2%.
I'm not exactly sure why your trying to reduce your temperatures by idling your CPU? Your temperatures should remain at a low temperature, even if your CPU is at full load for extended periods of time.
I've said this on the forum many times, but I do not personally recommend overclocking. At the very least, overclocking can seriously reduce the life of your CPU, and in some cases (if care is not taken), end it altogether!
The temperatures you listed above are already ten degree's or so below it maximum temperature threshold, and this is when it is most idle?
Are you able to take picture of the inside of your PC, so that we can identify any potential overheating problems? Also download speedfan from here: Download SpeedFan - Access temperature sensor in your computer and post a screenshot of the results?






























