A4 PCV Valve Problem?

[Macca1815]

Hi everyone,
Just hoping for some advice. Today I was driving my 2010 Audi A4 1.8TFSI when I noticed an awful squealing sound coming from my engine bay. I noticed that the sound gets quieter when I accelerate in drive and is loudest when the car is idling (in drive). Revving the car in neutral just makes the sound louder. I got home to try to diagnose it and noticed that the noise stops completely when the oil fill cap is off. However, when the cap is off, the engine constantly jumps between 800 and 1200 rpm (surging?). There is also strong suction on the oil cap, as its very difficult to take off and there is an audible pressure change when I take the cap off. I figured it might be an issue with the PCV Valve, but I was wondering if anyone has any other ideas or if you agree. I have also gotten a P0171 (System Too Lean(Bank 1)) fault code a couple of times before but have never noticed an issue with my fuel trim when recording data using an OBDII scanner. It currently does not have a check engine light.

Any help would be appreciated :)

[Smac770]

Probably the diaphragm in the PCV pressure control valve. There's a round cap on the PCV, on the backside of it should be a pin hole. If you cover that, does the sound go away and the idle smooth out?

You could just get the Dorman repair kit, which is a diaphragm and spring and cap. Use only the diaphragm. It won't last as long as latest OE rev PCV diaphragms will, but it's also only $30 or so.

[Macca1815]

Yes, there is a whistling sound coming from that pin-hole, and covering it smooths out the idle. I'll give that a go. Thanks for the help!

[Smac770]

Dorman 917-064, at pretty much any auto parts store around here.