Need help with possible diagnosis...
 

I have an issue where my 2004 Concorde LX (2.7 liter) will work fine for days or weeks, with the engine light off, then the light comes on. The car will still usually work fine until the light goes off days later, but occasionally, the car idles rough in gear, then struggles to accelerate, and sometimes the engine light will start to flash. (only happens when the car is first started, once the problem has been worked through by restarting a time or two, the car will be fine to the destination) But if I pull over and shutt it off and wait a few minutes, it seems fine again, but the engine light is still on.

The codes I get are a P0300 (random misire), and a P0158 (02 sensor 2, bank 2). I have in the past also gotten the evaporative emissions code... P0400 or something. It makes sense to me that if some cylinders were occasionally not firing, that would explain the lack of power, but then wouldn't the 1st 02 sensor before the cat be triggered?

I also know that a bad cat converter could cause the power issue, and would make sense to trigger the 02 sensor after the cat, but can converters actually work for a while, then act up, and then work again? I also suspect a vacuum leak, but I don't know if that could cause this whole mess. In the winter when cruising at speed, a whistle will develope, but it will go away by either slightly incresing or decreasing the throtle, and this only happens in sub-zero temps.

I know that a vacuum leak might cause the evaporative emissions code, but could it cause all this other stuff? Sorry for the long post, but I would really like to get this finally resolved, thanks for any help or advice you might have.