Well I just disconnected two fuel injectors to try and coax the 1500 RPM down to attempt to temporarily trick the ECM into a relearn to fix P0507, (got that from a blog post by a Nissan Tech), sounds kinda not right, I thought I would give it a try anyway. I also put my hand inside the intake just fwd of the MAF to restrict airflow to get the RPM even lower, the engine would not stall, I then jammed a big towel into the intake and completely blocked it, the engine still runs at 500 RPM with a fully blocked intake and with two fuel injectors electrically disconnected. I had done this same thing a few days ago but without any fuel injectors disconnected and it always stalled out when the intake got about 75% blocked, but with the two cylinders not working the engine is now able to run from an unknown vacuum leak with a fully blocked intake.
I did a propane test and spray water test while the engine was running in this condition, noticed a slight RPM change with the water being sprayed between the intake manifold collector and the intake.
I will have to go back and research this: I had read something somewhere about how this engine has as part of its emissions a process that recirculates some of the exhaust back though the intake? Maybe this is why the engine can still run in this condition? Can it run by sucking air back up the exhaust in this limited no load operating condition?
My first assumption would be no, but the more I read about these new engines, I cannot assume anything until I find a reliable source to set me straight.
I will try and hunt the exhaust process info down, I hope I am wrong and it is not the case. Then I could have actually found a diagnostic starting point, a vacuum leak that effects both banks? Maybe, because I disconnected two injectors on B2, I will redo the running engine condition and disconnect the 3rd fuel injector on B2 to notice any difference. Then do the same to B1.
I just tried to repeat the same condition, every time I started to fully insert the towel into the intake pipe it would stall, I drove the PF around again after reconnecting all fuel injectors, just as I did the first time, same result: a stall.
I disconnected that 3rd fuel injector after doing the towel blockage test and there was an obvious change.
I did the dollar test to the tail pipe to see if it was sucking air: it was not.
Maybe the water I poured on the intake stopped up the vacuum leak, especially if it caused the intake gasket seal to close up temporarily, will go out and try to replicate it again in the AM.