1997 lincoln town car 4.6 with a p0430 fault code

I will make an assumption here, we know what the root word means. This code was extracted from the computer by? What this is telling you one of 2 things: The Bank 2 oxygen sensor down stream of the catalytic converter (there are 2 converters, one for each bank of cylinders on the 4.6ltr engine) is bad and/or that the Bank 2 catalytic converter is no longer doing the job it was designed to do. Simply, Catalysts wear out. They are good for approx 100,000 miles (as required by Federal Law). Again, I assume that the reason the intake manifold was replaced was because it had a crack in one, or more, of the runners? (part that feeds the head of a manifold). It may have taken a while to find this as being the cause of why the car running incorrectly, maybe rough. This means, that during the time the car was being driven with the problem, the amount of unburned, or not within spec exhaust gases, coming off the side of the engine affected by the intake issue was higher than normal. This out of balance level of exhaust gases were being dumped into the converter on that side of the engine, thus causing the converter to have to run hotter, work harder, or even at the time the gas was being processed through, causing deposits to be formed in the converter, thus shortening it's life span. The Bank 1 side of the engine, apparently, did not have the issue and it's catalytic converter's life was not affected. I hope this makes sense to you.