Stalls randomly

Hi I have a 98 pontiac bonneville 3800 on 130,000 miles, drives like a dream when it does, it stalls when I approach lights, sometimes even while driving normally after about 15 minutes, most of the time it doesnt start up immediately, I have to sit there for at least 30 miutes before it starts. When it stalls it gives spark but wont turn over. Had fuel filter changed. What else can you recommend.
thank you
michael