Toyota Repair: Toyota Avalon 2000, mass airflow sensor, phillips screws

Question
Dear Ted,
I need your advice, please. I have found two codes using a diagnostic tool and wanted to know if they are related and what is the best way to resolve the problem. The first code is P0171 "Fuel System Too Lean (Bank1). This code appears twice. The other code is P0420 "Catalyst Efficiency Below Normal (Bank 1)." Please let me know what I should do - thanks, I really appreciate your help.
Regards,
Jorge Farias

Answer
The P0171 code is usually set by a dirty mass airflow sensor (MAF)sensor, it's located on the intake pipe just after the air filter look for two phillips screws and an electrical connector, it can be cleaned using some electronic cleaner is a spray can, remove the sensor and spray inside the opening where the sensor wires are, spray until the wires are clean and look like chrome, let it air dry and reinstall it, the two wires with the bulb on it is the air temp sensor and does not cause this code. Take care of this first and clear both codes, the P0420 is a catalityc converter code which can come up because of the lean/rich condition, wait and see if it comes back, there is agood chance that it won't.