mod_status is a great way to track down the source of high CPU usage and to find what vhost/script is the cause of it.
It gives you a live view of bandwith usage, CPU usage, and memory usage broken down by domain/vhost and script/URI.
Enable mod_status
vi /etc/httpd/conf/httpd.conf
ExtendedStatus On
SetHandler server-status
Order Deny,Allow
Deny from all
All........