Freise

I don't know if this is even a problem but have no idea where to start and seeking advice.

2005 enthusiast purchased in 2013
The idle has never been what I would call buttery smooth. After it warms up, the rpms at idle will drop to around 650, about every 10-20 seconds,with no specific pattern. It returns to 750 shortly afterwards without "searching" for idle. There is an audible difference in the exhaust note. Never affected me in any way, has never given me a problem, just a little bit of burble and a drop to 650rpm. I've seen discussions where the Z has not been known for having a super smooth idle, so I've never given it much thought.

The other day I was messing around in the Torque app while waiting for work to open the gate, and I notice that every single time I get the "burble," it is reporting "Open loop due to system failure" in the fuel system status. My assumption is that there may be a problem somewhere in the O2 system, but obviously it is not a sensor that has taken a total dump. No codes either, and although open loop makes me think an O2 sensor, all four appear to be giving consistent voltages to the ECU, at least what I can gather using the app (I'm skeptical in my confidence due to the frequency of the data through an app!)

Tl;dr Car going into open loop at random intervals at idle according to app, doesn't seem right but never been an issue