Nissan Repair: Mass air flow sensor, mass air flow sensor, infinity qx4

Question
I have a 2001 Infinity Qx4 that reads that it needs an Mass air flow sensor. I had it checked out and it works fine except it keeps turning my maintenace light on.  My wife is worried that something else could happen while the light is on and we wouldn't know what happened. There is no indication that anything is wrong as far as performance. I put a K&N performance filter in it about two weeks before I had the problem. A manager from Autozone said the filter may have had too much oil on it and fouled the sensor. I cleaned it, he turned out the light, then it came on after several miles. A Nissan mechanic said I should not use those filters, but I like the performance.  I was thinking of shopping for a used sensor since they range in price from $200 OEM to $400 Nissan replacement. the part # is 74-10072.  I took the battery cables off to reset the maintence light but the Nissan mechanic said I have to turn it off with his test equipment. I am confused but want to save money. Help

Answer
I suggest you remove the aftermarket filter off because they do nothing for performance. The engine is tuned and the computer set at the factory to run with the stock apperatus. You can use that stuff on cars pre-computer but unless you can recalibrate the chip, it will not work and the computer will continue to make adjustments to compensate for the reading. It will go into "Calculated" mode where as the computer will try to guess the air flow and adjust the mix accordingly. Even if you purchased 10 MAF sensors, it will do the same thing.