1994 Taurus stalls in hot weather

I have a 1994 Ford Taurus V6 140,000 miles. 4 times now I have been driving in hot whether with the engine warm and the engine will stall. It happened three times last summer and I put of doing something about it this winter until this spring when it happened on a hot day. It doesn't cut out immediatly but will "cough" a couple of times then die. It won't restart immediatly but after cooling a couple of minutes it will start as if nothing had happened. The first time it happened I was right in front of a mechanics shop. He plugged it into the computer and it said that nothing was wrong.