I think I have cured the engine stumbling i used to experience at higher
elevations.  I never had the problem at lower elevations.  I most
recently experienced the problem in december on a trip to the eastern
sierra, where the elevation of the main highway (395) ranges from about
5,000 feet to 9,000 feet.  The problem was at its worst during a fairly
heavy snow storm.  I also experienced the problem in january on a ski
trip to the Lake Taho area, where the roadway elevation there and
en-route ofter exceeds 6000 feet.

based on the experience of others, I cleaned the contacts on my air flow
meter and replaced the O2 sensor in an effort to correct the problem.
To clean the AFM contacts, I had to pry the black plastic lid/box off of
the AFM (it is glued on).  Once i got the lid off, I sprayed pretty much
everywhere with contact cleaner...esp. at the contacts...I also cleaned
the carbon track with a Q-tip...and the contact area of the contact arm
by very carefully rubbing a clean piece of heavy paper across the face
of the contact until it no longer left a black mark on the paper.

I again sprayed everything with contact cleaner...used low air pressure
to gently clear out the excess contact cleaner...and then re-glued the
plastic lid/box with silicone.  I returned today from a several day trip
to the eastern sierra...same places as before...it even snowed once like
last time...there was no hesitation/stumbling at all... there always has
been on each of my 4 prior trips to the area in the last year.  The
engine also seems to excelerate better.  Hopefully the cure is not
temporary and will last awhile...

steve
1990 syncro westfalia