I've had the stat off and bathed it in boiling water. The pin was all the way in, flush with the brass cylinder it protrudes from. A few minutes in boiling water had it out to around 5mm proud of the plastic housing (10mm from the brass cylinder).
I popped it back on the Pierburg but the problem remains, still idling at 3000 for 5-10m before dropping back to ~1000 :(
I did however find a stray lead hanging out around the carb. There is a set of three connectors routed together along the firewall under the green vacuum sphere. Two of these are connected to the driver's side of the carb (pictured / pointed out) but I have a third from the same group just hanging loose. Anyone have any idea what this is supposed to be attached to? I thought it was just a ground, but it has a male spade terminal and two wires.
Any help much appreciated!
(sorry about the pictures...)