Oh, my gosh ... I'm looking at my records right now ... first time I saw the P0430 was back in November of 2004 when my '97 Taurus GL wagon had 108,598 miles on it. I saw it again in October of 2007 at 148,286 miles. So it's come and gone.
The one that's been consistently with me (seemingly) FOREVER is P1131. Started in 2002 at ~ 80,000 and I've never been able to get rid of it. The CHECK ENGINE light is always ON and it's always there. People say it's probably a vacuum leak, but I can't find it. Probably should just replace ALL the vacuum hoses to see if THAT gets rid of it (probably wouldn't cost that much), but I just haven't done it.
Sometimes I think these Fords just have their computer parameter bands set to narrowly. IOW, if they had just bumped the trigger points out a little bit more, we probably wouldn't be seeing a LOT of these nuisance codes.
How long have you had the code P0430 and it intermittent or continual. I have a intermittent P0430 on a 98 WIndstar with 3.0 and trying to determine if it is the converter or upstream 02 sensors getting lazy,etc.