TOYOTA 4RUNNER OBD1 CODES CODE 52

I Had A Valve Job Done On My 3.0l V6 4runner (167,000 Miles) Because The Engine Was Running Rough And Getting Lousy Gas Mileage (13mpg) The...

I Am Getting #52 (knock Sensor) And #71 (egr System) Codes. I Can’t Find Solutions For These Repairs, Any Suggestions?