brushie_

I've been digging around for threads about this oil cap, I feel like I'm missing something when it comes to how it's used or how exactly this thing releases pressure in the valve cover. I have the latest oil filler cap with the F at the end of the part number that comes with a new gasket, and got a new gasket that sits on the ring around the oil filler cap.

Before this, I smoke tested the engine for vacuum leaks and only found smoke coming out of the filler cap. My car would idle somewhere between 600-800 RPM and would definitely feel like a vacuum leak, jumping up and down in that range. Turning the AC on would make it vibrate and jump way more. Sometimes with no explanation, the idling RPM would rarely sit itself back up to 800 RPM flat and feel as smooth as it should, with AC as well.

With this new gasket and cap, at first it would do it but now it's back to making vacuum leaks from the filler cap. I've pushed on the part that tends to cause the problem (top part of the gasket that sits on the ring on the valve cover) and can feel the RPM changing. Am I just missing something or is suppose to do this for releasing pressure?

Panzer A4

It sounds like your breather system (aka PCV) may be clogged. You can unclip some of the tubing looking for either dried oil or sludge. Blauparts sells a replacement kit.

brushie_

It's a brand new hose set. replaced all the PCV tubing and vacuum lines about 3 months ago. Unless they can clog that fast.

I've also tried to clean out the routing inside the valve cover itself as much as possible when I replaced the gaskets a while back.

Panzer A4

Did you replace the "S" hose to the valley pan under the intake manifold? Mine had a plug of dried oil that had to be scraped out with a screw driver.
You shouldn't have vacuum or pressure under the valve covers at idle.

brushie_

Yeah I don't know why it's sold seperately from the bigger PCV tubing set since I'd imagine you'd want all of it replaced at the same time. If it's that tube that goes under the throttle body then yeah that's replaced.
I believe there isn't really any pressure/vacuum coming from the oil filler last time I had it off to check. I'll probably take off that hose you mentioned and check if it's already backed up with crud or something.