Toyota Repair: Error Code P0420 and P0505, toyota corolla, failure code

Question
QUESTION: I have a check engine light and I took the car in for a scan check. I got error codes P0420 and P0505. I cleaned the MAF sensor with CRC cleaner, by the time I drove 11 miles, the check engine light came back on. What do I do next. Please help because I don't want to waste a precoius money doing guessing work. Thank you.

Dave

ANSWER: What year and model is it, what engine does it have and how many miles on the odometer?

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QUESTION: It 2001, Toyota Corolla, I don't know if it VE,CE, or LE because I just bought it and the label was missing. It has 127,000. It drives great. The transmission shifts well and picks immediately you engage the gear. It is a four cylinder 1.8L.

Answer
The p0420 is a catalityc failure code, it's fairly common at this mileage, the converter should be replaced, the p0505 is an idle control control system malfunction, try cleaning the inside of the throttle body with a brush and some air intake cleaner.