Thats what I thought about the engine braking too. But then I thought it out, when you let off the throttle to let the overrun fuel cut engage, the IAC will open to its last good position + dashpot adder anyways, (usually about 45 for me). Do not close is doing the same thing, but instead of closing while driving and opening on let off, its staying what it was while in PID control and adding the dashpot when you let off. For me it required playing with the step adder number but its working very well now.