2001 GT obd2 problems

[joec44]

I tryed the search but no help 2001 GT 120K mi. my friends car last tech charged him %500 and then gave up. codes p0300 p0301 p0303 p0171 It seams to me like a lazy O2 sensor it was reading .03 volts at idle after car was hot I was just ready to change it when it started to work kinda voltage jump around for a wile then just die also runs rough cold will do a comp. test next week any help would be cool also ware is the frount O2 pluged in at the wire just goes into body but I can not find the end

[Bitter]

clean or replace mass airflow sensor.

[joec44]

MAF was replaced by last guy was reading about .5 pounds a min may be after mkt. shoul I get a fractory unit