How to troubleshoot Fast-CGI / PHP failures

Hi,

I have been dealing with a strange issue that is affecting a web server we manage.  The server is:

AMD

Windows 2008 SP2 x64

IIS7 FastCGI PHP 5.3 (and 5.4) - all installed via WPI

There are times when the server becomes unresponsive via HTTP.  We are still able to reach the console.  A restart of IIS causes the server to return to a normal state.

There are error messages in the Event Log showing that FastCGI has stopped executing, but there are no additional details.

We run FastCGi/PHP in the app pool, there are no other types of code being executed.

There are no errors of any consequence in the php error logs.  I see this in the event log:

Log Name:      System
Source:        Microsoft-Windows-WAS
Date:          12/23/2012 8:06:33 AM
Event ID:      5013
Task Category: None
Level:         Warning
Keywords:      Classic
User:          N/A
Computer:     
Description:
A process serving application pool 'DefaultAppPool' exceeded time limits during shut down. The process id was '2608'.
Event Xml:
<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
  <System>
    <Provider Name="Microsoft-Windows-WAS" Guid="{524B5D04-133C-4A62-8362-64E8EDB9CE40}" EventSourceName="WAS" />
    <EventID Qualifiers="32768">5013</EventID>
    <Version>0</Version>
    <Level>3</Level>
    <Task>0</Task>
    <Opcode>0</Opcode>
    <Keywords>0x80000000000000</Keywords>
    <TimeCreated SystemTime="2012-12-23T13:06:33.000Z" />
    <EventRecordID>378415</EventRecordID>
    <Correlation />
    <Execution ProcessID="0" ThreadID="0" />
    <Channel>System</Channel>
    <Computer></Computer>
    <Security />
  </System>
  <EventData>
    <Data Name="AppPoolID">DefaultAppPool</Data>
    <Data Name="ProcessID">2608</Data>
    <Binary>
    </Binary>
  </EventData>
</Event>

ALso this:

Log Name:      Application
Source:        Application Error
Date:          12/23/2012 1:40:15 AM
Event ID:      1000
Task Category: (100)
Level:         Error
Keywords:      Classic
User:          N/A
Computer:    
Description:
Faulting application php-cgi.exe, version 5.3.12.0, time stamp 0x4fa94d46, faulting module php_wincache.dll, version 1.2.614.0, time stamp 0x4df7de26, exception code 0xc0000005, fault offset 0x00005bb0, process id 0xf84, application start time 0x01cde0ce61d00557.
Event Xml:
<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
  <System>
    <Provider Name="Application Error" />
    <EventID Qualifiers="0">1000</EventID>
    <Level>2</Level>
    <Task>100</Task>
    <Keywords>0x80000000000000</Keywords>
    <TimeCreated SystemTime="2012-12-23T06:40:15.000Z" />
    <EventRecordID>56171</EventRecordID>
    <Channel>Application</Channel>
    <Computer></Computer>
    <Security />
  </System>
  <EventData>
    <Data>php-cgi.exe</Data>
    <Data>5.3.12.0</Data>
    <Data>4fa94d46</Data>
    <Data>php_wincache.dll</Data>
    <Data>1.2.614.0</Data>
    <Data>4df7de26</Data>
    <Data>c0000005</Data>
    <Data>00005bb0</Data>
    <Data>f84</Data>
    <Data>01cde0ce61d00557</Data>
  </EventData>
</Event>

Sometimes the site just sits there and never responds.

I don't know the next step in troubleshooting this.  It seems like there is a stuck PHP script or process which causes fcgi to die, but I'm not sure how to dig further to find out what is causing it.

Can anyone help me identify things to check on my server to look a little deeper into the problem?

Thank you.