Hi KE7FNS,
First, if your CPU is running @100% capacity, you better check the running processes instead of available File System space.
Use 'top' to check which process is causing your problem.
There is a known problem with an upgrade process causing high CPU load.
Use 'top' and check for a process called "UNATTENDED UPGRADE".
If it is on your Pi, than kill the PID and run sudo update, sudo upgrade manually.
Next reboot your Pi and check if the CPU is running at normal load again.
Best 73,
Bert PE1KZU
-...