Took my 2006 vw jetta 2.5l to autozone to find out about my engine light being on. code p0300 came up and some others that go along with this. what would be next step.thanks to any and all that reply.

SOURCE: 98 mercury villager OBD I code P0135

This code refers to the front oxygen sensor on Bank 1. The heated circuit in the oxygen sensor decreases time needed to enter closed loop. As the O2 heater reaches operating temperature, the oxygen sensor responds by switching according to oxygen content of the exhaust surrounding it. The ECM tracks how long it takes for the oxygen sensor to begin switching. It the ECM determines (based on coolant temp) that too much time elapsed before the oxygen sensor began operating properly, it will set P0135.
Repair short or open or high resistance in wiring harness or harness connectors.
Since you have already changed out your O2 sensor (as long as you used to OEM replacement and not the "Universal" replacement) you should not have to replace it again. You might check your thermostat to part of the time it takes for the O2 sensor to start switching being based on coolant temp, if your thermostat is not operating properly, it could cause the coolant temp to take longer than what is considered by the ECM to be normal.

SOURCE: 02 jetta has 4th cylinder miss!

Hi, what engine is on your Jetta ??

SOURCE: Engine light on 2002 VW Jetta

sorry , but no good news, if you are using a fair amount of oil it has most likely reclogged the converter. unbolt the pipe just before converter and run car, if it seems to run better then it is time for a set of rings and another new converter

SOURCE: 2006 vw jetta tdi service engine light reset

With the key in the ignition (but not turned), press and hold the Odometer Reset Button on the right hand side of the panel. While still holding that button, turn the key (although not far enough to start the engine) and then press and hold the Minute button on the left side of the instrument pane(if pressing doesnt work try turning the knob clockwise until service light has gone off and skip the pressing)l. Release both buttons at the same time.

SOURCE: 2004 VW Jetta 1.8T

Loss of power? How many miles? Plug, plug wire or ignition coil(if seperate poles) would be my guess.