Are you using one or two squirts per two engine revolutions? Is the management sequential or batch injecting? Also, surely the tuning resolution must be more accurate than 100 us?

Upto a point you could play with the ignition timing at idle to retard it a bit so you can idle with a higher map value. You can also try to lean it a bit at your idle speed and richen a bit just below your idle rpm, so if it tries to stall or run bad, then it will pick up again. Same with timing too. A rising rate fuel regulator will also improve the situation a little.