Bleeping computer folks helped me a couple of years ago. I hope someone can assist me this time.
Symptoms: Slow computer, especially noticed when on online. Videos freezing, sites slow to open, etc.
Tracked this to System Idle Process running around around 90% CPU. It jumps around from high 60s to high 90s, but centers around 90%
Installed Process Explorer and found that a thread running behind System Idle Process seems to be the problem, running at 40-50% CPU on each of the two processors. The thread is consistent: ntoskrnl.exe!KiCpu<address>
Poked around and found on various forums that ntoskrnl seems to cause this problem, but the specifics following ! vary. Generally, it seems if I can Identify KiCpu and turn it off, that will solve the problem, but am at a loss of how to do this.