New IAC Valve and no change.

Let me try to be a little more detailed in my explanation of the engines behavior. When the engine is cranked, the idle immediately jumps to 1,500 rpms and runs rough. As you drive down the road, you can feel the roughness of the engine through a choppy (stumbling) characteristic. After you have gotten the engine warmed up, it may (or may not) begin running smoothly, as if you had thrown a switch. Choppy and then immediately smooth, then of course, back to rough. It will fluctuate like this as long as you drive it.

When you come to a stop, the idle may be @ 1,500 rpms or 500 rpms, just no way of knowing until you stop. Check engine light flickers quite a bit, and occasionally stays on for long periods and stays off for long periods. I have not been able to get any codes though. It flashes the 12 code once, sometimes twice, and then just goes out.

Because of the way the engine behavior changes immediately and not gradually, I don't think it is a fuel related problem (I could be wrong and frequently am), it seems more like an ignition problem.

Please, any help would be appreciated. I don't want this thing to whip me and send me to a mechanic.