Bank 1

Bank 2

Hello all, I have a stubborn 2006 G35 coupe (6mt) that I've owned and drifted for 2 years now. Ever since a couple weeks after I bought it, it's been having an intermittent stalling issue. I’ll push the clutch in, and the idle will drop way below 750 or sometimes straight to 0, my gas pedal won't work, and the engine will either stall or revive itself after a couple seconds (50/50).

This issue is completely intermittent, sometimes the car will drive fine for a couple days up to a couple months, then it will become undrivable, then eventually “fix itself” and be fine again. There are also no DTCs or check engine light. Here recently it has gotten more common and worse. Sometimes it will stall mid-turn resulting in the steering wheel locking up, which has been scary and almost caused a few accidents. It also sounds and feels pretty weird sometimes when I go to shift, whenever it's having this issue.

When the issue gets bad and the car is “undrivable”, it will struggle to start and sound like it's almost running on half cylinders, it also puffs out black smoke when moving at low RPMs, which makes me think its a fuel related issue (possibly regulator or injectors?)

The only known issue with my engine is that my Bank 2 Intake VTC actuator makes a slight rattle at around 3000 rpm. I've always thought that maybe it could be my issue, possibly getting stuck and not changing timing when it's supposed to, but I've had others tell me not to worry about it.
Parts I've replaced trying to fix this issue (ALL PARTS ARE OEM) :

-Replaced all 4 Camshaft sensors

-New Gas Pedal

-New Crank Sensor

-Replaced IPDM/all relays and fuses

-New Throttle Body

-All new intake gaskets

-Cleaned inside plenum

-Smoke Test for vacuum leaks

-Idle relearn procedure

-ECU Reset Procedure

-New MAF

-New coil packs

-New spark plugs

-Replaced one O2 (threw a code randomly, replaced and didn't affect issue)

-Sea Foam treatment + Injector treatment

-Cleaned all engine bay grounds (that I could find)
Only performance mods are intake, test pipes, full 3 inch exhaust with a single resonator. Upgraded Z1 clutch with lightweight flywheel. I'm pretty positive the flywheel is not causing the issue, it was happening before replacement and all bolts are marked and torqued to spec with red locktite.

On the thought that the issue is fuel related, I recently pulled my spark plugs to check their condition, they are NGK one-step colder (NGK PLFR6A-11) and have been in for 6000 miles. Any help, recommendations, or thoughts are wanted and welcomed.

 

Those plugs look a bit, black.. Is that ECM tuned for the 'test pipes'?
Colder plugs are great for forced induction, i'm not sure how a NA engine benefits from colder plugs..
You mentioned you've been drifting this car which means high RPMs which lead to more engine wear (colder plugs, i get it now) so could be mechanical wear issue..
First thought in my head when i see 'test pipes' is that the O2 sensors are not properly doing their job unless the ECM is tuned..