Question

I got the engine codes P0304 & P0325 on my 2002 Mercury Villager

Answer 1

Have you ever had the spark plugs and distributor (cap and rotor) replaced? If not, I would start there 

try to replace the spark plugs and distributor (cap and rotor) since 

p0325 is a knock sensor and might come on due to the P0304.

if you fix the p0304 and the knock sensor code is there replacing the knock sensor (see picture below)