2007 Ford Focus Stalled at light

Ok I have a 2007 ford focus 446xx miles, I was stopped at a traffic light and the engine just shook a little then stalled. Turned right back over with no problem and hasn't done it again. Now, this exact same thing happened once with my old sunfire, I replace the air filter and all was fine. I discovered that the air filter, so to speak, is supposed to last a lifetime or something and you can't really change it. So, my questions are these, could that still be the issue? If so how can I check it to see? Also, if it is supposed to last a lifetimedoes that meani should take it to a dealership and they will takecare of it? And if not what else should I consider?