Processor one core at 90%?

[Mark_Twain007]

So I have a computer I built about a year and a half ago I think. Specs are:
Intel i7 950 @ 3.07 GHz
Asus Sabertooth X58 Motherboard
GTX470
12 Gb of Ram
About a week ago I noticed that my processor status told me that core 6, hyperthreaded so the second half of core 3, was running at 90% even though I had no programs running. I checked my processes and I can't find anything wrong. System idol processes is at 99%. I noticed that the temp on my Core 3 is a few degrees higher than on my other cores.

I have also noticed some problems when playing graphically intense games like Mass Effect 3, or even Mass effect 2, sometimes I notice a lag that has never been there before. Does anyone know how I could fix this?

 

[unksol]

it may show 99% idle but it also says 10% CPU usage below. Don't look at the %. click on view, and add CPU time and sort to find the offending process

 

[aicom]

Something is definitely running one strong thread that's eating up your CPU time. That's certainly what's causing the lag. More than likely you've got some hung program just spinning on your CPU.

EDIT: Actually try enabling "show kernel time" (or something like that) on your CPU time graphs. It should be in one of the task manager menus (view or options I think).