First I took at look with Activity Monitor but nothing obvious in My Processes. So I switched to All Processes to see what root processes were doing. Bingo, a nondescript Process Name called kernel_task was eating up just over 100% (110% before turning off some apps).
I read this article (Kernel_task process taking up an inordinate amount of CPU) at MacFixIt, which indicated to start cleaning stuff up (ya, I knew that, housekeeping).
First I uninstalled some stuff that sounded good but which I just never use:
Ok, CPU usage on kernel_task now down to about 104%.
Then I brought up the System Preferences -> Sharing panel. In here I had Bluetooth sharing on for a previous project but I am not currently using it. So I turned that off.
Bingo! Kernel_task is down to about a peak of 4% CPU usage now in a steady state (ie. when I am not opening new processes).
The basic gist is that kernel_task is a catchall for a multitude of system processes and hence it can take some rooting around playing with settings to get it to decrease. Good luck.