Apache CPU Utilization issue....

Having Apache CPU issues where we are maxing out pretty powerful VPS. Webhost has been less than helpful on trying to track down the offender. They are saying PHP is soaking up resources. Wondering if there is anything you can do to help me assess what's going on with CPU utilization or see any plugins that could have AJAX interaction issues? Any advice is appreciated. I'm at a loss for how to really troubleshoot this given some of the plugins I'm using are critical for the site to function.