Engine Management Warning Lamp

Help! My EMW warning lamp comes one occasionally, then goes out. The manual says that this is a Canadian warning, just the outline of a car, with no words. I have had it in to the dealer twice and they have reset it, but it still comes on occasionally.
I have checked the tightness of my gas filler cap, but that doesn't seem to have an effect.
Should I ignore this nuisance?
Jill in GA