Update:

I cut the wiring harness open right by the valve cover.
It looks pristine inside. The wires are even flexible. It does look a bit newer than the other components (rubber cover is very supple) so I'm guessing it's a replacement.

I also cut the harness to the Electronic Throttle Actuator open and the wires there also look fine.

Since I've still got the intermittent stalling and idle hunting issue I suppose the next step is cleaning the MAF, the throttle body and running the codes.

Thanks again for the help.
Ian