sitting at red light the check engine light comes on

My car idles below 1000 rpms when I'm sitting at a red light and the check engine light comes on and it gets low and starts to shake to the point of where its about to turn off, but when I drive it pass 2000 rpms the check engine light goes away and it doesnt come back until lower rpm?

I've tries using chevron fuel treatment, but it didn't help. My idle is flipping out, it goes above 1000 rpms but never above 2000 unless I drive it past 2000. It has a v8 engine.