Kernel_task slowing down my iMac!

Question

I have noticed that more often my iMac is slowing down with me seeing the spinning beach ball every time.  Pulling up Activity Monitor I see that every time a process called kernel_task is using up between 50% to 80% of my CPU.  Then it will drop off suddenly...and go back down to 1.4 % or lower.  I deliberatly kept Activity Monitor open so I could observe this.  I unplugged all of my peripherals and externals and restarted my iMac.  The problem persisted.  It doesn't seem to be linked to any specific third-party application, I saw that iStat Menus and PopCharX were showing up in Console a LOT so I uninstalled them - but the problem persists.  It is getting very annoying!  More often than not I notice it when I try to use Quick Look, but it also can occur when trying to select the Application list in the Finder, when trying to load a web page in Safari, and at other random times.  I know that kernel_task is a kind of "catch-all" for some system processes, but Apple engineers REALLY need to address this issue.  After reading the threads on the site here I see this has been a problem going as far back as 2005!  It has been blamed on everything from temperature to graphics issues.  Everyone has a solution, not all of them work. 
Pretty frustrating!  If anyone has had a problem with this, and has a viable solution, please let me know.  If anyone knows of an application or terminal command that would allow me to at least look inside the kernel_task process to see a log that would be awesome (it would at least allow me to narrow down the cause of the slowdown).

Answer 1

Please read this whole message before doing anything.
This procedure is a diagnostic test. It’s unlikely to solve your problem. Don’t be disappointed when you find that nothing has changed after you complete it.
The purpose of this exercise is to determine whether the problem is caused by third-party system modifications that load automatically at startup or login. Disconnect all wired peripherals except those needed for the test, and remove all aftermarket expansion cards. Boot in safe mode and log in to the account with the problem. The instructions provided by Apple are as follows:
Be sure your Mac is shut down.
Press the power button.
Immediately after you hear the startup tone, hold the Shift key. The Shift key should be held as soon as possible after the startup tone, but not before the tone.
Release the Shift key when you see the gray Apple icon and the progress indicator (looks like a spinning gear).
Safe mode is much slower to boot and run than normal, and some things won’t work at all, including wireless networking on some Macs.
The login screen appears even if you usually log in automatically. You must know your login password in order to log in. If you’ve forgotten the password, you will need to reset it before you begin.
Test while in safe mode. Same problem(s)?
After testing, reboot as usual (i.e., not in safe mode.)