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