1990 Buick century stalling.

I have a 1990 Buick Century 3.3L v6, I've been having problem with it stalling while it idles, as well as when I have the headlights on and come to a complete stop and then push on the accelerator it will spit, put, choke and almost always stall. When the headlights aren't on, it will usually just spit, put and choke and then be okay, but sometimes it will stall then too. I've cleaned the idle sensor, and I've replaced the crank positioning sensor, mass air flow, electronic spark control and the O2 sensor. The spark plugs, alt, starter, battery and vacuum lines are fine, so I know it's not those for sure. I could really use some help.