Once decel fuel cut is active, the ECU keeps the injectors off until engine speed falls to the value in the Min RPM table. At that point it brings fueling back and the engine runs normally again. The table can be mapped in up to three dimensions, so the exit point can change with other conditions.
Why the exit point moves with RPM rate
The Nexus also looks at how quickly RPM is falling. When the engine is coasting down slowly, like a gentle decel in gear, cut can safely continue to a lower RPM, because there's time to bring fuel back smoothly. When RPM is dropping fast, like a free rev in neutral, cut ends at a higher RPM so combustion is back before the engine falls through idle. That's what stops the stumble or near-stall you can get when fuel returns too late.
Its second job: O2 control
The same table also affects closed loop O2 control. Above the Min RPM value, when the ECU sees zero demand (foot off the pedal), closed loop fueling is switched off. Combustion is unstable in those conditions, and trying to trim fuel from the oxygen sensor reading would only add error.
Our starting point
Set Min RPM comfortably above your target idle so the engine never arrives at idle without fuel. If you feel a jolt or see RPM dip below idle as fuel returns, raise it. Pair it with a sensible cut delay time, and see the main decel page for the rest of the setup.
