Mass air flow sensor problem persists

After about 300 miles of driving, the service engine light came back on. My brother has an obd tester, and it showed, again, the mass air flow sensor as the problem. He turned the light off, and when I drove it today, after just a few minutes, it came back on and stayed on for the 140 drive home from his house to mine. I filled the car just before I left his house, and then filled again when I got home. 135 of the 140 miles were highway, and my mileage was only 20.42, and my speed varied between 65-75, as the speed limits are different in Ohio and PA. This mileage seems low to me, as I was the only occupant in the car, and other than an overnight bag, the car was empty. I had new plugs installed last week, and was hoping my mileage would be in the almost mid 20 range like it was last year when I drove to Florida. Does this issue have anything to do with the mileage? And, any thoughts on how to fix the problem? The shop cleaned the sensor last week when they put in the plugs. Thanks, Mark.

This is just my opinion and nothing more,I would change your sensor out with a known good one,that is if you have another one or someone would be good enough to lend you one. As far as fuel mileage,I believe the Mass air flow sensor could be responsible for poor fuel mileage,because if it was not functioning properly it could be giving incorrect data to the PCM and the PCM could be adjusting the fuel supply more or less than it has to. Another thing air temp. plays a large part in getting good fuel mileage, I believe most gasoline engines get their best fuel mileage at about 70 degrees F and I at least know in South Jersey it was no where close to 70 degrees. ed