1993 2.3L Codes, need some advice.

[KerrMD]

First post but I love the forum already. Seems like a very helpful crew.

I just got a 1993 Ranger XLT 2.3L with A/C from a buddy of mine who had bought it for his grandchild that cannot drive a manual.

I did a KOEO test and got the following codes.

539 System shows voltage at PCM pin 10. NVM on this one. Defrost was on durring the test.
157 MAF signal is/was low or grounded.
158 MAF sensor is/was high or short to power.
172 O2 sensor not switching. System is/was lean. Single right or rear HO2S

I pretty much figured that the MAF needed to be replaced or at least cleaned. Am I looking at an O2 sensor replacement as well as a possible MAF replacement?

The 539 code is the one that has me confused.

I've reset the codes to see what pops up in the near future.

Thanks for any and all advice.

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Alright, I've done some research (as I should have before posting) and have come to the conclusion that it is, most likely, that my air filter needs replacement and the MAF sensor needs cleaning. I think this would cure the whole darned thing,