HELP. Getting this code on my 2002 protege 5,(P0421). 100,000 miles. Replaces plugs, replaces wires, both sets, whole egr valve (BRAND NEW), all vacuum hoses, O2 Sensors front and back (NEW). Erased check engine light went to smog and said FAILED because couldn't complete OBD self tests. Have to drive 80 - 100 miles and bring back. What gives. Any suggestions. Please don't say CAT. YIKES.