Stalling 5000cstq

[Gary Kaklikian <Gary.Kaklikian@digital.com>]

Any advice on this one would be greatly appreciated:

My 86 5kcstq runs fine 99.9% of the time (believe it or not). So, like any
good German car, it decides to act up when conditions are poor - nighttime,
blowing snow, sub-freezing temperatures. Driving home on the freeway in
these conditions at sane speeds - 25-35mph, 2nd-3rd gear - car is running
fine. Suddenly, hesitation, lack of power, stalls. Car starts fine, depress
accelerator, car misses and has barely enough power to stumble forward in
first gear. So I stop, let car sit for 10 minutes, starts fine, and continue
on my way. Get to a gas station, fill the tank (was half full before)  and
put in some gas line anti-freeze. Back on the road, and about 5 miles later
- same thing happens and after car sits for a few minutes, it's fine for  a
while again. This occurs several times, but I finally limp home, unlike many
more unfortunate people would spun off the road in these conditions.

Is this evidence of vapor lock and/or water in the gas? Ignition components
appeared to be dry and car started fine after stalling each time (though it
idled low and threatened to stall unless I let it sit for a few minutes). Of
course, driving to work this morning in sunny, but sub-freezing conditions
car ran fine again.

TIA for any suggestions,

Gary Kaklikian
86 4kcsq (turbo soon)
86 5kcstq