Fortunately for you if you can find a good technician that can diagnose, most things can be fixed.
If this vehicle is carbureted, I would start there. If the choke is stuck or there are problems internally with the carburetor then you need to find someone who really knows carburetors to fix it.
If it's fuel injected then there are many things to check. EGR, vacuum lines, exhaust restrictions. You may want to see if the catalytic converter isn't clogged. This would be okay cold, but once it got hot it could cause the vehicle to stall out.
This is not an easy thing to diagnose so you'll have to find someone who knows older vehicles and is willing to invest the time to find out what's really wrong. Good Luck.
〉 Answered on Aug 25th, 2007 by Lori Johnson, Owner and Instructor at Ladies Start Your Engines