Yeh, it does look like it goes into idle control. The only thing i can find that currently determines the idle condition is the TPS idle threshold. I would think you could use Kpa as a refference point, IE when kpa is below 20kpa, engine is in over run. as the engine speed drops, drawing against a closed throttle, the MAP starts to rise as you get close to 1000rpm, i can see it on the logs.
If this is going to be implemented and i think it should (pleading to the code boffins
), IF it were me, I'd be calling it 'over run threshold Kpa'
As it stands, the more i think about it, im going to adjust the throttle stop so TPS read 3% with the stepper at zero. Only because i cant see it working any other way with what we have