P0420 1997 Honda Civic -

Question

1997 honda civic hx p0401 has been on cleaned out plate and holes into intake under injectors seemed to run fine for a few weeks then code came back on and p0420 came up too fuel milage dropped and seems suggish on acceleration when warmed up

Answer 1

"has been on cleaned out plate and holes into intake under injectors seemed to run fine"

I'm not sure what you mean does not make sense.

p0401 is a EGR, remove the EGR and its piping and clean it, its probably clogged with carbon buildup

P0420 is for the catalytic converter, check for exhaust leaks before doing any other replacements