Had this exact same thing happen on an '86 Jetta.  Problem was that one of
the air intake boots had a hole in it in a place where you couldn't see it
(on the back side).  The intake vacuum would just barely lift the plenum and
the car would start after lots of cranking, then it would die when turning a
corner (plenum would have g-forces on it).  If you need these boots let me
know because I can get new ones for a good price.

Thanks,
Ken Wilford
http://www.vanagain.com
John 3:16
Phone: (856)-765-1583
Shop:   (856)-327-0027
Fax:     (856)-327-2242