1997 expi and ecu code p1131

ok so I have scanned my ecu because I am tired of staring at my cel and found the code P1131. The code says that it is a air fuel metering device which I thought could be either MAF or O2 sensors. However I don't want to replace all four o2 sensors just to find out it was either only one or none of them which threw the code. Anyone who may have some knowledge of this please help.

It is bank 1 sensor 1 lack of switching. This sensor is on the passenger side in front of the converter