Your PCV system routes blow-by gases back into the intake. It only works
correctly with a closed and properly sealed system.

----- Original Message -----
From: "Don Hanson" <dhanson928@GMAIL.COM>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Friday, July 24, 2009 11:50 AM
Subject: No Oil filler cap=poor idle..observation on Digifant..

>  My van has an inline four VW motor..Digifant II injection, lots of the
> same parts as a WBX.  So yesterday I was changing the oil (to 20-50 dino)
> without changing the filter...I do that every second change..3000 mi (+/-)
> intervals.  I was distracted during my refilling and somehow I spaced-out
> replacing the cap on the filler.  Started it up and had a really poor
> idle...very similar to what was going on just before I replaced my Idle
> control valve (about 4000mi ago)  I was puzzeled, thinking "Jeeze, feels
> like some connector has come loose"..but I wasn't even inside the engine
> compartment and it happened suddenly without any hints before the oil
> change.  Then, standing behind the van scratching my head, I noticed my
> licence plate a bit askew and found my oil filler cap wedged in there
> rather
> than on the filler pipe.  Put it back on and re-started...in about 10
> seconds, the idele returned to normal...
>
>  So, there must be some kind of vacuum supply that's dependent on a sealed
> sump, right?  Anyone want to try to explain why leaving the oil filler cap
> off might cause the engine idle to go all wierd...kinda felt full rich..
> though it was so windy in my Gorge driveway that I couldn't see any dark
> exhaust or smell anything..
>
>  Don Hanson
>
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