At risk of covering checks already made, it doesn't appear to be an "adjustment" issue as there's no response to turning the air screws.
With size 40 idle jets this should be happening and clearly it's not. That's the issue, seems that idle jets or circuit is impaired (that's fairly normal if left for years etc) making any refinement redundant until you've got flow going.
In effect the elevated idle is having air that doesn't get paired with any fuel to give correct running when you shut the throttle. If it just gets enough revs going it will start to gradually draw through the main jet supply just sufficient to keep it running lean at those revs.
If the idle jet delivered fuel competently it wouldn't rise and also give you a response to air screw too.