PHP code causing very high load.  Assistance with cause / diagnosis

Morning, I am hoping that some expert here can shed some light on how I can find out why some PHP code is causing very high load on a Linux server I have. The code is a Trillium Chat/forums board written in PHP.  There are times of very high load that it causes that are un-usually high.  Like 500% increases and more from time to time.  I have put on the IONCube PHPA but that did not seem to help. Some of the PHP has been modified and more added.  I am wondering if there is any software available that can look at it to find loops, bad coding practice,etc, that might cause this. Any other reccomendations on what I could do to optimize, anyalyze etc. this? Assistance appreciated. Mark