Andy, umm I've changed the CAT on it and still got those CO readings.. but there is no guarantee that the replacement CAT actually worked either. It was off a car with kind of worn piston rings, probably contaminated with oil loads.

Tabetha, its a 1999 VW Polo.. as per my other emissions thread(s) lol

I'm not sure about many fords, but I know the ignition timing on this polo isn't actually adjustable.. as the ECU adjusts it really fast using MAP and Knock sensor readings.

I've got a feeling one of these sensors may be giving false readings..