I assume you have looked at
http://www.k-jet.org/articles/information/k-jet-in-detail/
We recently re-furbed the Kjet on the 242gt, so have been through what you are going thru.
The items that control idle are - Aux air valve and control pressure regulator. the first is always in action, the second only does its thing when that engine is cold. ( acts like a choke after startup )
First thing I would check, is that assuming the Aux air system is clean, there may be missing or loose or blocked vacuum lines that control it. sometimes people work on these and don't know about the aux air valve, so they muck around with the throttle stop. check that the black knob actually is the thing controlling the idle speed.
We had the fuel distributer rebuilt. luckily our control pressure regulator appears to work, but these can also be rebuilt.
we found that the air fuel mixture inside the fuel distributer is very finicky. that is, there is not much difference between run and not run, perhaps one full turn of the allen key. I set ours to as rich as it would go to the point of stall, then backed off a quarter turn. still gets great economy, and runs nice. I set ignition timing a bit more advanced than the recommended 5 degrees ( about 10 now). and we tested by ensuring it revved well but does not ping at all.
not sure what cam you have, but the gt likes to idle at 1000 when warm.
hope some of this helps.
