Toyota Repair: 2001 prizm/corolla check engine light, air flow meter, fuel air mixture

Question
Dear Ted,
I know that you are really knowledgeable and really helpful to most of the people who ask questions here.  Please shed some light for me.
I have a 2001 Prizm(I know it rolled off the same assembly line in the NUMMI plant where they manufacture the Corolla).  We just purchased this used with 63K on it. It is the 4 speed automatic and we currently have 64K on it.
No repair had been done to it.  the latest maintenance was cooling system flush, transmission oil and filter change, motor oil and filter change at 63800 about 3 weeks ago.  I was on a trip that is about 120 miles away.  The road condition was uphill and downhill.  The check engine light came on and stayed on during the trip.  Drove it to my mechanic after the trip and the code read was P0171 bank 1 too lean.  My Mechanic said it was most likely hard acceleration up hill and on the downhill, when the gas pedal wasn't press as hard, it triggered the computer.  Does that make sense at all?  He reset the computer and said if it comes back on, I should then get the O2 sensor replaced. otherwise, I should not sweat it. I read about cleaning the MAF sensor for this code, do you think that it could have prevented the Check engine light caoming on?  If I don't clean the MAF sensor, do you think that the uphill /downhill driving condition or any other condition could cause the same problem down the road?
Does it pay to clean the thortle, injector and engine with seafoam/cleaner?

Thank you in advance for your help.
Regards,
Chris C


Answer
No, it's not the O2 sensor or any of the other stuff, the
PO171 code indicates a lean fuel/air mixture which is caused by the MAFsensor also known as the air flow meter, it's located on top of the air intake tube near the throttle body, remove the connector and the two phillips screws and pull it off then clean the inside of it with some electronic parts cleaner, spray it to the opening, there are two platinum wires inside that pick up dirt and get coated with it after a while and then give wrong air flow reading to the computer, make sure these wires are cleaned so they look very shiny, also replace the air filter, if it has an aftermarket filter like a K&N or any filter that is sprayed with oil etc., get rid of it and put the toyota air filter back in. Remove the negative battery terminal and wait about ten seconds then reconnect it and that should fix the problem.