Nayeon

Ok so this is gonna be a huge wall of text so please bear with me. I am looking for opinions on an idling issue that I have on my 350z (77k miles) and I have already tried many things to solve it. The problem is that at idle (when the car is warmed up) the car would dip down to about 400-500rpm as if it is about to die and would rev itself back to about 1k rpm to prevent itself from stalling.

I suspected that it could be a dirty mass air flow sensor and/or because my car had is catless so the car might be running too lean due to too much air flow. What I did was I bought new oem MAF sensors and got the car professionally retuned on the dyno to accommodate my mods. The car was running smoothly and perfectly after the tunes.

However, my tags are due to expire soon and I needed to do emissions and I know I can't pass due to the CEL light being on for no cats and my tuner said that he can turn it off by disabling the rear o2 sensors and that it would be pointless because the car would not be obd2 ready and would not pass emissions anyways. So my other option was to put in o2 spacers in the rear o2 sensors (post cats) in the car to trick the computer into thinking that there is enough of an air flow difference to think that the cat is still there.

Fast forward I put the spacer in and everything and I reset the ecu and went through 2 drive cycles and the check engine light is off and everything but the idling issue came back and my fuel trims are completely ****ed. In this picture(https://imgur.com/a/CIj2S) you can see that bank 1 is adding 25% more fuel at idle (which is the max amount that it can add I believe) and bank 2 is adding about 12% at idle.

Would spacing out the rear o2 sensors too much be causing this issue? I would think that because the o2 sensors are detecting less air, it would think that the engine is either running normal or rich and would be trying to take away some fuel rather than dumping an insane amount at idle. I was also thinking that it could be an o2 sensor issue in general because I have completely replaced all of the o2 sensors on bank one because when this problem first started, it was only bank one that was affected. It could also be a dirty throttle body and I was going to clean it soon to see if it would help. Also here is a picture(https://imgur.com/a/W5uDY) of what the fuel trims and o2 sensor voltages looked like right after I added the spacers. This picture is completely what I expected it to look like after the spacers (bank 2 has original o2 sensors so it could be reading a little differently from bank 1 but it is still within reason)

The first picture was after about 50-60miles of driving and after I reset the ECU. Normally I would just take the spacers out and this would solve everything, but I was curious as to why the ECU is acting the opposite of what I expected to with the spacers on.