Hi there.
Just reading this post and hoping your still around from 2009. I have a 2001 996 Biposta experiencing the same issues. You mentioned that" Turned out to be a partial break in one of the ECU wires near the multiplug."
I'm having the same problem with a temperature sensitive short. Wondering how you went about finding it in the wiring near the ECU multiplug?
Cheers!
DucSailor26