Air intake input circuit low

Some "codes" are stored in the vehicles memory and can only be removed by equipment that can communicate, i.E, two-way communication, with the computer. If you are only "reading" codes, simply removing the negative battery terminal may not remove this code. Many codes that have to do with emissions are stored this way. I would suggest having someone with a scanner that can "tell" the computer to erase this code, do so, then rechecking.
The other cause of this problem could be a dirty intake port, especially if dirt carbon, or oil are laccumalating in the area around the sensor.
"Decarbonizing" the intake may help this also.