I'm having a P0135 (I think it is P0135, its the code for the pre-cat O2 sensor heater circuit) come up intermittently. I will clear it and sometimes it will come back after 20 miles, sometimes it will take 150 miles. I ran live feed on my OBD2 scan tool and watched my O2 voltage and Short Term trim and both seemed to be responding and not going out of whack. I also heard that a faulty MAF could cause this code (don't know how), so I monitored that too while driving and it responded normally.

I have a 1.8t engine and am using a universal Bosch O2 sensor.