My 2001 S-type is misfiring at idle and at normal/highway speeds. There is not a check engine light, but the following codes showed up P0460 and P1233. Any thoughts on the possibility of it being the fuel pump?

Get a COP (coil on plug) tester and check each coil at idle and swap out offending coil(s) doubt if its the fuel pump.

+1 on testing or replacing the coil units.

Quite often engine oil finds its way into the spark plug wells and causes the coil units to short. When you remove the coils, check to see if there is any engine oil present. If so, the cam cover gasket and spark plug seals will need to be replaced.