PHP5-CGI & CPU Load

[Mastacheata]

Sounds like a php script gone wild.
As you are using fcgi every user should run its own php process and therefore it might be very easy to identify which user and which script is running mad there.

Try finding out which php process causes the extreme cpu load and then you could look at the parameters of this special php-fcgi process for identifying the script with the error.
It's highly unlikely that there's something wrong with php itself.