I'm chasing down power loss between 1.5k and 3k that throws no codes and seems to be worse when the engine's warm.
I've been educating myself about the PCV Valve thinking maybe that's to blame, and I came across this video, which suggests a symptom of a failed PCV valve is vacuum in the crank case/valve cover at idle - the PCV valve is failed open, letting the intake pull vacuum on the crank case when it shouldn't.
Sure enough, when I go out and pull the oil cap at idle, I hear a solid hiss as the pressure equalizes.
My question is, is that normal? Is vacuum in the crank case just stronger when the valve has failed, or is any noticeable vacuum a solid indication of a failed PCV valve?
EDIT: N51, FYI.
EDIT: Oh also - no engine codes, per se (lean, persistent misfire, etc). I did get one misfire, once, under load while the issue was acting up. And I do have a code for the secondary air injection system, which can be caused by a bad exhaust mix since the pre-cat O2 sensor is how the secondary air system verifies functionality.