Ford,I have a engine miss codes po174 po420 are on now I had code multiple cylinder miss fire. I changed spark plug wires and plugs l

I have.a engine miss I have codes po174 and po420 now. I had code first said multiple cylinder miss fire I changed coil unit didn't get better changed plug wires and spark plugs.

My car has 252000 miles.
My car has an automatic transmission.