After about 6 weeks of troubleshooting, I finally solved an issue w/ my 2008 iMac 27″ where apps would run at high CPU, pegged until I needed to hard reboot. No matter what app, it didn’t matter… all browsers, Lightroom, TextEdit, iTunes… all pretty weird. Time Machine hung while indexing… ANYWAY….
http://www.rdoxenham.com/?p=259&cpage=1 Posted about Apple kernal extensions that were meant to reduce heat, but sometimes fell into a bad loop. The blog details all the assumptions, but all I needed to know was to remove a single plist file to fix it.
cd /System/Library/Extensions/IOPlatformPluginFamily.kext/cd Contents/PlugIns/ACPI_SMC_PlatformPlugin.kext/
Then locate the file to remove from within that folder. It will be a file that describes your product number.
While this seemed to work for a short period of time, the real issue was bad RAM. I removed one of the 4GB simms, and voila!