I have a 97 Golf K2 edition w/ 130,000 mi. on it. I just replaced both O2 sensors and now it has popped 1 Fault code and one Pending Code. P1128 (Long Term Fuel Trim, System too Lean) and P0131 (Low Voltage System 1 Bank 1). I've checked the pins on the O2 sensors for corrosion and made sure that the pins are making contact and every thing looked good. I'm going to go and get some MAF cleaner and see how that works.
Does anyone have any other ideas. Thanks

 

im sure you re-set the computer after the O2 sensor replacement, this will allow the PCM to reboot itself and it will go to a self test mode to see if the condition that triggers the original code(s) still exist.
for the lean condition, you might consider replacing your fuel filter. it's also possible that the fuel injector is clogged up, you can try one of those concentrated fuel system cleaner that you add to the gas tank