Tom,

I think I can explain for you. This mystery has to do with crankcase ventilation, and emissions.

Your crankcase is hermetically sealed to disallow oil vapor and un-spent emission products from making their way out to the atmosphere. At the tippy-top of your motor, you will see a round black gizmo with a fat hose running to the intake. The black gizmo is your PCV valve, that is Positive Crankcase Ventilation.

That valve and hose are constantly sucking waste gases out of the crankcase, and burning them during the combustion process. You'll notice that that hose connects to fuel injection system downstream from the air flow meter, and upstream of the throttle valve.

Therefore, any air that enters the intake air stream through that hose is technically, un-metered. The fuel injection system, realizes that there will be some air and vapors coming in through the PCVvalve, and is design to take that into consideration.

If the rubber seal around the dip stick is not seated in its housing on the tube, a constant air stream will leak into crankcase, and therefore into the intake air stream. Theoretically, this will make the motor run lean.

In essence pulling the dipstick will make the motor run less than perfect because un-metered air is making its way into the intake air stream. Removing the valve covers does the same thing, as does drilling holes in the top of the crankcase.

Comprendez vous?

G. Matthew Bulley Bulley-Hewlett & Associates www.bulley-hewlett.com Cary, NC USA 888.468.4880 tollfree

-----Original Message----- From: Tom Young [SMTP:young@SHERLOCK.SIMS.BERKELEY.EDU] Sent: Monday, April 26, 1999 10:42 PM To: vanagon@GERRY.VANAGON.COM Subject: Re: Update: 81 Air-Cooled Vanagon Stalling at Warm Idle

On Sat, 1 May 1999, Eckie Prater wrote:

> >Recap: I was experiencing a stalling problem when the engine was warm and > >dropped to idle from running speed. It was also difficult to restart. > >In addition, I was experiencing a lackluster performance overall, lots of > >'hiccupping' (which I now know as 'missing') and generally slovenly > >acceleration. > > My 82 air cooled had the same symptoms as above. > I think it is one of the reasons the PO wanted to sell it. > It had the tune up and a Petronics point replace module installed. > Guess what? If the dip stick was just a little loose in the dip tube > air sucked into the engine case. Ran like a big vacuum leak. > If you push the dip stick in to the seal, problem solved.

I'm sitting here trying to figure out why a loose dipstick would cause the engine to run poorly, and I can't. I frequenly find my dipstick tube out slightly and I've never noticed and poor performance when it's that way, or any improvement when I push it back in.

An air leak in the FI system can give you running problems for sure, but the dipstick tube just opens into the case, so it's not the same thing.

Anybody have any rational explainations?

--------------------------------------------------------------------- Tom Young young@sherlock.SIMS.Berkeley.EDU Lafayette, CA 94549 '81 Vanagon ---------------------------------------------------------------------