Your post is somewhat confusing, 100% isn't idle, and are you using task manager or something other monitoring program to determine this...? Whatever the case here's an idea to at least figure out what program might be causing the problem. Try opening task manager and going to the processes list. You should be able to sort the list of processes based on CPU usage, set it to show the most power hungry processes at the top and then let the computer idle. IF it works the culprit should pop up near the top when a load is put on the CPU and you can hopefully write down the name. Seeing as you don't know what's doing it I can't suggest any further steps, but hopefully that will help you determine which process is causing the issue.