Just found this on the net:
http://www.kalmaker.com.au/page40.html

Good explanation of why the cars hunt and carry on at idle.
Also an explanation on the next page on how to fix it if you have an aftermarket ECU.

Makes me wonder if theres anyway to trick the ECU into giving more timing advance, and possibly pull out a little fuel, and then rig up a microswitch or something to do this only at idle.

Cheers,
Dave.