iMac Kernel Task at 100%

Very strange problem with our iMac. It kept one CPU busy at 100% with the kernel task spinning like crazy and takes 10 minutes to boot for some reason. Here is what I learned on the web on diagnostic procedures thanks to CNet:

  1. Well unfortunately, a virus is the first thing you worry about now that Macs are more popular. So Comcast includes Norton with every subscription so the first trick is to go through the entire hard drive looking for things. Nothing there.
  2. Do a disk utility check on repair disk and repair permissions to make sure the disk is OK. Nothing there.
  3. Remove all the login items and also everything running because a run away application is the next target. Nothing unusual there.
  4. The kernel task has got these kext things which third party drivers so it could be anything so turn off everything (Drobo, Canon printers, network, Minolta 5400 II scanner). That didn’t help.
  5. Now try to do a safe mode reboot which runs at limited mode. What you is to shut down the machine and when you do a startup and hold the SHIFT key on, so it boots with minimal drivers. The problem is still there.
  6. Now start Console (go to Spotlight to find it) and look at messages there. I see something that says IODevice not working and so it looks like there is a low level problem.
  7. Reset the PRAM. This doesnt work often, but you again turn it off and then press start and hold four keys down COMMAND-OPTION-P-R and then it will cycle again. This actually fixed the problem! 
  8. But if all the above fails, it looks like a complete rebuild is the only solution, so I hope that you kept the OS X Install Disk to do this. In my case, I stupiedly skipped #7 and ended up with a rebuild system that still had the 100% kernel task problem! Oops!
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