Help w/diagnosis - specific idle problem on 99 Accord
 

I have a 4-cylinder 99 Accord with a180,000 miles that has always run well
and is fairly well maintained. Recently developed a problem that first
turned up after driving 430 miles without stopping, the last leg of a 2000
mile road trip during which the car was fine.

When I stopped for the first red light off the Interstate, the engine died.
Since then, it's the same every time. The car runs normally during warmup
(including idling at correct level) but once it reaches operating temp, the
idle speed seems to dip to zero. Sometimes it will splutter and hold on at
about 250-300 rpm but mostly it dies, especially when stopping in traffic.

So far I've changed the plugs, which were ready to be replaced but not
severely worn. Any thoughts on where to look next for a fix? I appreciate
any suggestions.