SPARK FLOP. a puzzle for a true Guru

[Rolley]

Hello helpful forum freaks

i have a random spark flop steady driving. its like someone flips a switch and everything kinda goes to zero including fuel trims.

what would cause this?

I also have my rough idle that i cant fix no matter what i do. ive attached the log also

any help or clues, is HUGELY needed

Thanks, fellas

[CaudleDynamicsLLC]

The big spark drops I'm seeing look like theyre correlating with DFCO, and only seeing it happen when the accelerator pedal position is zero and fuel system status is in OL/Accel/Decel.

I didn't find one in a quick scroll through, but is there a particular timeframe in the drive log where the spark is dropping with the throttle still steady (and greater than zero)? If not, it's just going into decel fuel cut off and referencing the corresponding spark table (and dropping the fuel trims as there is no fuel being injected)

[Alvin]

Looks like just dfco to me.

[CaudleDynamicsLLC]

Pertaining to the idle surging:
Only applicable if youre running an auto trans but, since this is a GenIII swap application and I've seen this cause idle headaches many a time, wanted to mention it: Definitely make sure the gear selection P/N vs R/Drive is being reported to the PCM. Since the engine load is significantly different in P/N vs. gear, if it cannot switch between the two different idle "modes" its going to chase its tail around trying to correct. May not be the case here, but gear selection wasnt in the log file for me to see so just wanted to mention it.