Located in California--I recently bought a used JDM engine with around 50k miles. ALL accessories, e.g. oil pump, water pump, timing belt, ALL seals, spark plugs & wires etc.....worth about $1k in parts were replaced w/Toyota parts. I did NOT go cheap. Original engine had 387k miles and head gasket blew. Took the 4runner to the smog shop and failed with "high" NO (nitric oxide); MAX allowed is 512 and MEASURED at 679.

What should I start doing first? Clean air flow sensor? Replace O2 sensor? I'm praying that it's not my Catalytic converter. The smog results printed/stated the catalytic converter PASSED?? Any input is appreciated.