I will scan for codes in spite of no CEL. The car was running very well up until the cold weather hit here in MA, so I agree that the precats are probably OK. In fact, in the fall I took the car on an extended highway trip and got over 30 MPG. Can the precats fail suddenly, or is it gradual? It definitely coincides with IMRC operation under heavy load , though. Do I have an intake manifold gasket leak? I would think that such a leak might cause problems at idle. The car idles just fine. My guess is that the cold weather has caused some plastic or rubber part to crack. I'll keep looking. It would be nice to completely eliminate the precats as a problem before my emission warranty expires in a couple of months.
Thanks for the reply. Did I read that right? 148K miles on your Duratec? You must have some stories to tell.
