I've read a good way to determine idle timing is to find the amount of advance with the highest MAP. I didn't do this but seems like a good idea. My idle timing bounces between 18-20 degrees based on MAP. I mentioned 13" of vacuum above, my Kpa to inHg calculation in my head was wrong. I idle between 58-60Kpa, that's 15-17". I'd imagine the best way to handle your low engine vacuum may be to adjust the tables to your real working area.
