2003 Nissan Sentra sputtering

When idling at a stop light car feels like it might die. Sputters like it is idling to low or struggling for gas. Two weeks ago car was sputtering as I was driving and check engine light was flashing. Code read it was misfire so I changed the spark plugs. Ran good for a week. Then started sputtering when I stopped at a stop sign. But check engine light has never come on. I cleaned throttle body, but that has made no difference either. I am out of ideas, please help