Easy one this time (hopefully) :-)

[dom14]

Haven't checked the choke break diaphragm but given the carb is effectively only a couple weeks old and it seems that the cleaner in the connector at least temporarily resolves it, I'm leaning towards a high resistance connection at this point.

I'm trying to source a new connector, but can't find a listing anywhere online, so I'm thinking an interestingly priced genuine might be the only choice... Another thought I had was to buy a new Deutsch plug and wire that up instead

If the choke flaps are slightly open when cold start the engine(only slightly) then it's quite likely the choke break diaphragm is working properly, or you can apply a slight vacuum to it to see if it affects the choke flaps to be opened slightly, but I probably wouldn't 'cos you can end up damaging these diaphragms by applying too much vacuum.

I am assuming you bought a brand new aftermarket identical carby off ebay.
These carbies come as suitable for both TB42 & RB30. IMHO, they need slight adjustment, tuning for each engine, even though
it is essentially the same carby, and I doubt the selllers do that on behalf of you.
My suggestion is to take it to a dyno & get it tuned properly or get yourself an AFR gauge kit and have it installed and tune it DIY.
Or you can get a Gunson Colortune spark plug and do it that way. I have both.
Adjusting the mixture without AFR or at least a Gunson plug is a bad idea for inexperienced DIY'ers like us IMHO.

In a nutshell, don't count the factory mixture settings that came with your new carby is ideal for your particular RB30.
Even for different RB30 engine's the carby AFR need to slightly adjusted for the engine to run smoothly.
This is why carby rebuilders generally prefer to have your vehicle with them, so they can tune it while fitted to the engine.

As for how all the above apply to your intermittent high idle issue is that such carby quirks can be very much related to other engine quirks.

It is even possible the primary or secondary throttle valves are malfunctioning regardless of the carby being brand new. You can find this by observing the throttle valve(s) from top of the carby while idling/revving the engine. Of course, I would wear safety glasses. You might need to stand on a chair unless you're seven foot tall.