I remember back in my early days when I was still running the 7747. I had a simmilar issue with the idle hanging like that, most noticeable at warm startup. I tried a few difffrent things before I got curious and changed a parameter called "IAC reset Vs baro" I was at my witts end. I started out reduceing them a bit, then I changed all to zero and it cured my problem. Not sure if it will have the same results for you, but its worth a try. Take and write down what values are in that table, then change them all to 0. That way, if it doesnt work, you can change them back.
Table is at 0x606. 42.xdf calls it "IAC reset Vs barometric" Marks 42-1227747-V4.3.xdf calls it "IAC baro reset"