[Zanthros]

Any new updates on this issue? You have taken care of many of the things that could have caused the issue. Intermittent/ re-occurring problems are some of the hardest to track down.Most people don’t have the skill set to solve just the basic stuff, much less this. You should feel good on the operations that you have performed as they are not for the faint of heart and more than just the work of a parts changer as they indicate a level of diagnostics and skill not found in the average person. The only thing that I could suggest at this point would possibly be either an electrical contract (plug) issue or possibly injector(s) issue. Without some live data it’s really difficult to accurately diagnose.

 

[Zanthros]

Agreed, live data is the key. Using your stft and ltft data you can probably diagnose most misfire issues. Other data like O2 and MAF data is also helpful. I had a similar issue and replaced the coils and plugs and it went away for about 50 miles, then bam, it came right back. Come to find out that one of the coils failed again. Been driving it around for about three weeks now and no issues! Manufacturing quality is not always what it used to be, regardless of who made the goods. I try to stay away from the dealership as much as possible because they are no better that a lot of the independent garages out there. Although difficult to find a competent shop they are out there.
Even a cheap scan tool that gives live data can be very helpful in diagnosing an issue like this.
I did make sure that I force triggered a “bad MAF sensor code” to clear out my LTFT and it was part of my repair. Of course I reset it and cleared the code to force a re-learn on that parameter.

 

[Zanthros]

I have the same or similar issue with my 2018 versa. Started with clogged cats( yes cats). There is an exhaust manifold cat and a cat after that.
Never got a cat code so never knew it was the problem until I couldn't go over 50mph.
Punched out both cats and car ran great for 2 months. Misfire came back and mph went down. Changed upstream 02 and mpg is back except for when the car is under a load or accelerating. Started toying with down stream 02 with fouler's and is getting worse. Going to the store to get new down stream 02 and test with and without fouler.
OBD2 says it's rich which I believe is coming from down stream 02 leaning it out.
Stft is running 0 to -?? . I think the random misfire is a fuel issue. It does not feel like a spark or coil issue. Misfire only occurs (flashing check engine light) at idle and stops flashing when driving.
It would be great to fix this POS because I am getting 35mpg + and 45mpg at 62mph drafting and vehicle.

What is your LTFT?
If it is normal then I hate to say it but look at your spark plugs.
You can reset the STFT and LTFT by forcing a bad MAF code. Disconnect the MAF plug (carefully) and start the car up and run it for a few seconds. Clear the codes and reconnect the MAF plug and your LTFT should be reset. Not you can get some accurate and current data to work with. That should help with the diagnostics part and hopefully point to the culprit.
Good luck!

 

[Zanthros]

Fuel trims are not what you'd expect on nissans. You may not get any changes with them. They use what they call alpha value, but you need a scantool with enhanced data to see this pid, so you can use the rear o2 and the equivalence ratio or lambda pids, which are your a/f sensor. These dont use an O2 sensor in the front.

If this is only occurring during idle, I'd expect a vacuum leak, misreporting MAF, leaking injector, or compression issue. With the car fully warmed up, and misfiring, what is the o2 sensor showing? You can tell if it's a lean misfire (fuel) or spark by watching this.

You can also introduce a small amount of unlit propane into the intake and and see if the condition improves, which would indicate a lean mis.

You can put a vacuum gauge on the engine and see if you have a steady needle with 17-21". If it's bouncing around, you have a mechanical issue, like low compression.

Good advice