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You can target 14:1 If you want the later model stuff with sequential injection does but being batch fired I stay richer to smooth out idle and they tend to rev nicer on throttle crack.as long as you get it away from 14.7 so it doesn't go into closed loop fueling at idle and surge you'll be fine. There's iac adjustments for how far from target rpm it can get before adjusting iac to compensate as well as the idle proportional spark to help stabilize idle if you have the idle spark advance set lower so it can gain torque by raising timing

In other software I always commanded 14.7 idle afr and never had an issue. Why would 12P be any different?

Because the OS triggers open loop mode for exactly target=14.7 AFR as that is where the narrowband should be functional to allow it. In factory tunes idle is not set to this.

Don't you mean closed loop?

Yes, i do

I thought so, typos are bound to happen