take it to your local auto parts store and have them run a diagnostic machine on it, it is usually free. I had the same problem with my car, I needed to replace the air filter because it was dirty and not getting enough air flow, also had to replace one of the O2 sensors, that the diagnostic found and car is running fine to date.

That could be your EGR valve (as your previous Q suggested). Whatever the cause, it sounds like you have a air flow problem.

If the EGR is hung open, it will cause your car to produce to lean of a mixture. That would definately cause the problem you describe. (See my answer to your last question to see how to make sure it isn't your EGR).

Your idle is set too low. It runs when you first start it because the automatic choke is open, feeding extra fuel into the system. After it gets warmed up, the choke closes and the engine dies. Just adjust the idle. It's controlled by a little screw with a spring attached on the side of the carburetor. If you turn it a quarter turn at a time you should get to a point when the engine is warmed up where it idles as low as possible without dying. Otherwise you'll waste gas.

I wanted know if you ever resolved your problem my car does the same. After it's been driven for awhile and then sits for 10 - 20 minutes it idles low and if I don't press on the gas it shuts off.

my rule of thumb is take it to a mechanic if it cost more than $1000 to fix buy a new car