I can't give you any personal experience regarding your particular issues with the idle dropping (in my experience it increases slightly), but I remember reading something on another forum (GQ owners forum) about rust holes (?) developing in the fuel lines (and allowing air to seep into the line) where they go around the rear diff housing. The recommendation was to replace the line with rubber fuel line.
Ahhh... Here it is:
Quote from GQ Owners Forum:
"I replaced my fuel lines on my 92 patrol as they where rusted through and sucking in air. The worst point on my patrol is where the lines go over the top of the suspension turret at the back. I just replaced with rubber ones rather than using metal again. Problem solved" /End Quote.
If it's any help, I've got my hand throttle set to idle around 700 - 750 rpm when hot. When starting cold, I turn on the aircon as this ups the idle to around 1000rpm and let it run for a couple of minutes. Rarely do I need to adjust the hand throttle. Plus I get the added bonus of circulating the air con regularly.
I try not to drive it stone cold, but if I have to (like the bottle shop's about to shut

) then I just drive it nice and quitely until it reaches operating temperature.