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Sounds like it was just a bad coil. The car doesn't know what kind is on there.

Now cross's your fingers and hope that p0420 doesn't pop up soon from the misfire!

For future readers, these don't have egr valves. The same effect is achieved with variable valve timing.
 

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There is still quite a bit that can be tested, bit at this point I'd recommend finding a local diagnostic tech to just tell you what it needs.

You really want to ignite everything you e done and follow the data where it leads, but it doesn't sound like you have the equipment to do this accurately, and it takes knowledge/experience to evaluate the data.

There is still injectors and compression that I didn't see mentioned. In theory I believe bad belt tension could cause the computer to think there is a misfire. How did you test for vacuum leaks?
 

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Live data IS the key to figuring this out. I'd order a cheap Bluetooth OBD2 dongle on Amazon or your favorite shopping site, and get an app to use it on your phone. I prefer incardrpro over others I've used and the whole rig will only set you back like $15. No need for any expensive ones like bluedrive or that despicable Fixd one.
 

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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.
 

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I think you're going to chase this in circles. There isn't an upstream O2 sensor, so I think the data is not something to follow. Fuel trims are going to mess you up here too, like I said, they do not respond like other vehicles. Look at the o2 values you posted, the a/f sensor doesn't oscillate like that at all. It stays right around 2.2v instead of moving between . 1 and . 9 like an O2 sensor. This is why we look at lamda or equivalence ratio for upstream and o2 for down.

What exactly are the code numbers you are getting, without the descriptions, since some code readers do not accurately describe the code.
 

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Disconnect the exhaust and drive it. It'll run better if it's still plugged, or replace the a/f sensor with a gauge. I made one out of a cheap vacuum/low pressure gauge and and I believe old spark plug threads (it's been a long time). It should barely have any pressure in the exhaust, a restriction will have pressure.

I'm having some trouble with the data, not being able to see it on a graph with rpms. The fuel imbalance code is usually injector related in my experience. It means that a cylinder is messing with the mixture, and it can tell by the pulses it's sending to the a/f sensor in the exhaust.

If I'm reading the data right, it appears to be running rich, but it's hard to say. Could be a leaky injector, or exhaust restriction. Anything under 1.0 on lambda is rich, over is lean. The o2 on these doesn't do squat until it's super hot, like been driven. Not sure if it's even possible to get it working at idle. You see about .27v ish on the tool until it starts working.
 

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A few more thoughts. If your cat is hogged out, the o2 should be oscillating like you would expect to see a front o2, after it's warmed up.

I don't trust the fuel trims because At idle, your total trim was like 18 (lean), but the a/f says it was 2.18v (rich). I'm not confident that the oud you used to get that info was correct though.

Let's only look at lambda for upstream and o2 for down. Pull a vacuum line and make sure lambda goes above 1.0 and o2 goes down to at least . 200. Then add propane and make sure they both do the opposite. This will tell us that the sensors are reading properly. Watch stft to see if you get correlating changes. Remember that the o2 has to be very hot or this won't work. The a/f heats up within a few seconds. If all of this looks ok then we can trust the sensors and the stft.

It looks like you already know that lean condition at idle that improves with rpms is a vacuum leak, very good. If we can trust the data we just checked, then use your propane or brake cleaner to spray around suspect locations while watching stft or lambda and watch for a rich spike. Graphing is ideal for this if your tool offers it. Not sure if this is how you checked for leaks before, but listening for a change might not work. I'd suspect an intake leak with your cylinder misses, but also pinch of the purge line and brake booster hose and see if you get changes.

If it's not a vacuum leak, you can swap coils, plugs, injectors to see if the problem moves, and while you have plugs out, do a compression test.
 

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A few more thoughts and possibilities, ha, I've wondered for a while if an O2 spacer would impact fuel trims since Nissan does use the rear sensor for some fuel adjustment. If it's being tricked, I'm not sure how it will react. I don't know if pulling it from the exhaust stream has the same affect as good cat o2 storage capacity, if that makes sense? Let me know how it responds to those forced rich and lean tests I mentioned before. If it responds and how quickly it does.

The other thing is that a rich cylinder can impact the compression if that cylinder if the walls gets washed down with fuel. If you end up doing a compression test, you want to hold the throttle open, and make the needle bounce up about 4 times, but the important bounce is the second one. It should be pretty close to the final number. If you have any low cylinders, squirt some oil in the cylinder and try again. It could be low because of wash down. I've seen people replace engine because of this. Heck, I got my current car for a deal because it was thought to have needed an engine because of this.
 

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Only that there could be a restriction in the exhaust still, after the cat. That's why disconnecting the pipe before the converter is good. It eliminates everything after it too.

I'd move the injectors around and borrow a compression gauge from a parts store for free.
 
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