# PCV Diagnosis through Oil Cap-Theres a vaccum cleaner in my valve cover



## Dabpy (May 1, 2012)

Ive seen a few threads on here about testing for a bad PCV by removing the oil cap while the car is running. Ive had a slight mis at idle to I tested this out: ****! There is a ton of vacuum in the valve cover and if I take the oil cap off sightly and put it back on the engine bogs like crazy.
The thing that boggles my mind is I just had the car in for the PCV and flap motor recall not 10 000Km's ago and already it seems the PCV is blown. 

Is this oil cap vaccuum issue a sign that necessarily the front PCV is gone ( This one:http://www.ecstuning.com/Volkswagen...05_2006_2007_2008_2009_2010_2011_2012/ES8209/) or can the rear do this as well?

Thanks,

Justin


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## Krieger (May 5, 2009)

having a vac at idle is NORMAL... its exactly how it was designed to be... vacuum is drawn on the head and block from the manifold via the PCV system...

:screwy:

you test it by taking the pcv off and trying to force air through the valve. if it goes through, its busted... if it doesnt, then your fine.


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## quietA3guy (Oct 12, 2007)

The flying saucer type thing on the PCV regulates the amount of vacuum in the crankcase.
If it fails too much vacuum is created causing oil to get sucked into the intake.

When my PCV failed the engine would start blowing white smoke out the tailpipe a couple minutes after starting to drive followed by a check engine light for the o2 sensor and engine surging.

Also on early 2006 FSI's like mine the rear PCV is just an empty tube. All the valves are in the front PCV.


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## Krieger (May 5, 2009)

My understanding is that the check valve/ diaphragm in the front PCV is more to stop boost from entering the head, not to stop/limit vac. It might limit it to some degree, but it is mostly for the prevention of boosting your crank case and head. :beer:


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## ihasmkv (May 4, 2008)

The check valve is what keeps the intake manifold from pressurizing the valvecover. The diaphragm is there to limit the amount of vacuum it sees.


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## quietA3guy (Oct 12, 2007)

Here is a diagram of the PCV I took from saabers's thread on PCV bypassing.










Notice the non-return valve on the left was moved to the rear breather tube in 2006 1/2.


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## quietA3guy (Oct 12, 2007)

OP, if your only issue is a rough idle I would lean towards it being caused by coil packs or carbon buildup on the intake valves.


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## blackvento36 (Mar 17, 2003)

Krieger said:


> My understanding is that the check valve/ diaphragm in the front PCV is more to stop boost from entering the head, not to stop/limit vac. It might limit it to some degree, but it is mostly for the prevention of boosting your crank case and head. :beer:


You can't pull manifold vacuum on the valvecover, it would suck all the oil out. One check valve stops boost from entering the PCV and ruining the vacuum regulator (diaphragm as you call it). The other check valve is there to stop the turbo from blowing into the PCV from the rear port. The later cars rear check valve is redundant.


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## Dabpy (May 1, 2012)

quietA3guy said:


> OP, if your only issue is a rough idle I would lean towards it being caused by coil packs or carbon buildup on the intake valves.


This in my only issue and although the rpms do not fluctuate it seems to be getting worse. It does also appear to be somewhat rhythmic though so im going to do the coil packs and see what that does.

Thanks for the help. Will report back.


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