I took my 350z to get tuned, and it was running lean (which was fixed with the tune)

I discovered the the previous owner had the PCV crossover tube detached and breathing open from the passenger side and plugged on the driver side. I have since replaced with a new PCV crossover tube which will now be equalizing pressure between the valve covers.

Is this going to throw off my AFR?

 

Idk you tell us. Are you reading rich now?

In theory yes it could and no it couldn’t. It’s letting air in and or out of your valve covers.

I’m going to bet on no, it’s allowing air into the sealed system, which could possibly put air into the cylanders during operation... but that’s not directly open to the cylinders so it should be making you run lean. What it should be doing is throwing oil all over your engine.