When you take the oil cap off you are letting a lot of unmetered air into
the intake manifold via the crankcase vent.

In the FI book there is a test to see if the vehicle's 02 sensor and ECU can
handle a lean mixture. The way you run the test is to take out either the
dipstick? or take off the oil filler cap to let in unmetered air.

Mark Ingalls
Nebraska City, Ne
85 GL 'Airheart'
75 Beetle 'Salvation'

>From: andrewbell <andrewbell@QWEST.NET>
>Reply-To: andrewbell <andrewbell@QWEST.NET>
>To: vanagon@GERRY.VANAGON.COM
>Subject: Re: engine stalls when oil cap is off, is this normal?
>Date: Tue, 29 May 2001 22:58:44 -0500
>
>Sooo... what is it if it does not stall when the cap is open? Vacuum leak?
>This may be a stupid question, but my '85 does not stall out with the oil
>filler cap off. Also normal?
>
>AB
>
>Joe Romas wrote:
>
> > Normal! Most all watercooled VW's are plummed this way.
> >
> > Joe
> >
> > ----- Original Message -----
> > From: "john tomljenovic" <zadar72@YAHOO.COM>
> > To: <vanagon@GERRY.VANAGON.COM>
> > Sent: Tuesday, May 29, 2001 7:20 PM
> > Subject: engine stalls when oil cap is off, is this normal?
> >
> > > Hello folks,
> > >
> > > When changing the oil on the westie before our trip, I noticed that
>the
> > > engine idles all over the place until stalling eventually.  Put the
> > > filler cap back on and things are more normal.  What is this happening
> > > and is it normal for the 1.9?  what is up with the VW ventilation
> > > system that causes this?
> > >
> > > About being more normal in idleing, the bus now is even better,
>during
> > > this episode with the filler cap, I noticed that the filler tube was
> > > cracked.  I wrapped tape around to seal this crack and the mild yet
> > > annoying lumpy idle condition my westie had, is now gone.  It might be
> > > worth looking into this area for those of you having idle problems.
> > >
> > > Happy Trails, john Tomljenovic...83.5 campmobile
> > >
> > > __________________________________________________
> > > Do You Yahoo!?
> > > Yahoo! Auctions - buy the things you want at great prices
> > > http://auctions.yahoo.com/
> > >

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