I experienced such a symptom that was caused by a bad fuel filter.  It
couldn't hurt to change it if it hasn't been done for a while.

David

On Tue, 26 Jan 1999, S Sittservl wrote:

> I'm looking for advice on a problem I'm having with my '88 Westfalia.
> I've seen messages from others with similar problems, but I'm not
> sure if quite the same thing.
>
> When I've run the van at highway speeds (70 MPH) for a few hours,
> the engine begins to drop around 300 RPM every once in a while,
> causing the van to slow abruptly.  After about 1 to 5 seconds,
> the engine returns to its normal speed (and the van jumps ahead).
> Occurances are anywhere from a couple of seconds to a few minutes
> apart.
>
> If I pull off and let then engine go down to idle speed, it will die.
> It has a little trouble restarting, but not too bad - I've always
> been able to restart it.  If I let the van "rest" a while - somewhere
> between an hour and overnight, I think - the problem goes away.
> (It will return after a few more hours of driving, though.)
>
> So far I've only experienced this in cold weather, but I don't know if
> that's affecting it, or if the problem just happened to get started
> in late fall.  Also, I don't know that "highway speed" is necessary -
> I haven't had the opportunity to drive the van for hours at a time
> at slower speeds.
>
> It's time to replace my oxygen sensor - could it affect this?
>
> Thanks for any advice.
>
>                                        -Steven Sittser
>