Why do you think there is no ignition while over running the engine? Now
there should be nu fuel if the engine is over ~1,3500 rpm with the throttle
closed but the spark plugs should still be firing. Now on an extended
downhill run using engine vacuum (not back pressure), air is still pumping
through the engine causing the head and cylinder areas to go cold. The O2
sensor will also go cold and stop working. Upon needing power the O2 sensor
is ignored for 30 crank revolutions after fuel delivery is restarted but
with the cold O2 sensor fuel mixture will be unstable and even over enriched
until the sensor is hot enough to work again. An easy upgrade for the 1.9 is
go with a heated (3 wire) sensor such as the 2.1 uses. Also the sensor
should have some type of insulator on it or devise a wind deflector.
Originally they had an insulator on them but all are missing by now.

Dennis

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Steve Williams
Sent: Saturday, August 13, 2011 9:51 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Infrequent symptom: inconsistent power after descending hill

At 04:41 PM 8/13/2011, Zach Hale wrote:
>... after descending a large grade ... It wasn't exactly jerky as much
>as it was like power was fading in an out. ... I was letting the
>back-pressure on my engine help slow me down going downhill as I always do.

The same thing happens to me in my stick-shift '84 Westy with a GoWesty 2.3L
engine.

I don't worry about it much.  I figure maybe the plugs get a little fouled
as the engine pumps with no ignition.  It clears pretty quickly.

But like you, I'll be curious to hear what others have to say!