Over the last 6 moths I've been chasing an Inconsistent AFR issue and I've realized that I'm completely lost and need help. The car typically starts and idles fine but after driving a few minutes the issue suddenly occurs, the car will go pig rich. I used to be able to get the rich issue to go away by going into boost a few times, but that solution no longer works. The car typically idles at 12.5 AFR and cruises around 15 AFR. When the issue occurs the car will idle at 8-9AFR and cruise at 11-12 AFR. I was able to remove the richness at cruise by enabling EGO correction, but so far an unable to determine the root cause of the issue and am unable to completely remove the issue while idling. I can remove fuel from my VE table to keep the car from dying at idle and turn the 8 Afr into a more stable 11 AFR, but when the rich issue goes away the car struggles to idle at 15+ AFR. In an attempt to fix the issue, I've replaced the fuel pump, fuel pressure regulator, coils, and spark plugs. Last year I had an idle issue so I replaced the Idle Control Valve.

Attached is a recording where during a single drive without changing anything.
Notable time marks:
0s: 9 AFR idle
574s: Car failed to idle and died
636s: 15-18 AFR idle
685s: 18 AFR idle
697s: 13 AFR idle
946s: 9 AFR idle
1396s: 10-11 AFR idle

I'm not sure if this is an electrical issue because the previous owner did put in a 1.6 dash and I can see the wiring has been touched. Also, the previous idle issue (it would idle at 3k rpm and not drop) was caused by a blown ROOM fuse.

Car Details:
97 Miata
MS2PNP
Stock engine internals
Deatschwerks DW100
new OEM fuel pressure regulator
FlowForce PNP LS coils
FlowForce 640cc Injectors
GT2560r

Any help or pointers would be much appreciated.

Potentially useful notes:
This started 2 weeks after the battery ripped free while the car was driving.
Sometimes after letting the car sit for a while, it will drive without issue for a day or 2.

 

Can you tee in a fuel pressure test port?

Seems like your idle PW is pretty low to be pushing 10:1 considering 640cc injectors. Wonder if your new FPR is hanging? Rolling into boost might be what it needed to unstick it.

 

I honestly haven't tried teeing in, but I'll give it a shot. This is the 3rd FPR during this issue. I replaced the original one with a used OEM one, and then replaced the used one with a brand new OEM one.