How do your plugs look? Pop them out and see if they're carboned up. I'm having a similar problem but mine sounds more intermittent than yours. When it idles poorly, it's bad enough to cause fowling of the plugs. I'm going to unplug the forward O2 sensor tomorrow and see if that does anything. Mine runs normally most of the time, but when it goes bad, it's bad. So when I try something and think I've fixed it, time is the only way to tell if that's true (and it hasn't been so far unfortunately).
Intermittent problems are always the most difficult to fix. But from what you've described so far, it sounds electrical as it always runs fine for the first 20 seconds.... I'd also recommend jiggling the wires at each injector, O2 sensor, TPS, IAC, harness grounds, and see if you can get the problem to resolve (or start happening as in my case). You never know what you may stumble across. Keep us posted!
