I would worry less about the PCM for the moment and more about the marbles in a can thing. When you're in the engine bay and holding the throttle open enough to keep it where it's happy at 1100, do you notice any noise that sounds like it shouldn't be there?

 

Is knock count different than knock retard? I have plenty of knock count but my knock retard is always zero...

 

Nope. Like I said, its only present at 500 rpm.

I'm trying to figure out what's causing it to drop the rpm.

Would a bad MAP sensor do this?

I have an Auto X-ray as well. If someone can tell me what to look for I'll try it.

 

Well, if the only problem really is a low idle then probably your IAC is maxed out and you need to crack the TB blades or drill an IAC bypass hole.

 

I found a .uni file (datamaster) from last year when I started having this problem.

http://members.shaw.ca/fbody_god/Gripdiag1.uni

Note the timing, rpm dip, and knock count. Bad knock sensor? Bad MAP? Or bad PCM?

 

Did you ever have any luck finding the problem?

I'm having a surge problem as well and came across your post.

Mine is actually at full throttle and inconsistent. Otherwise runs perfect.

Anyway - just curious. Sounded like a timing issue.