Why does my car die at random times?

I have a 2000 Chrysler Cirrus V6. 217K miles. Lately i have noticed that it tries to dies at random times. Sometimes when going down the highway it goes all the way down to 0 RPM and than shoots back up. Sometimes when I'm idle it tries to die. I have replaced the Idler Air Control Valve and taht didnt fix the problem. What could be the problem?