I have a 2002 Audi A4 3.0L Quattro. Over the last couple of months the idle in the car is erratic. Sometimes when you crank up the car it idles fine and other times it idles very ROUGH. My first reaction was the the spark plugs or ignition coils had gone bad. I figured the best and cheapest way to start was to replace the spark plugs. I went down to the auto parts store to pick up the NGK Platinum Plugs, however, before I checked the codes to be sure that it was the plugs. Here are the codes that came up:

P0300 - Random Misfire
P0301 - Misfire Cylinder 1
P0302 - Misfire Cylinder 2
P0303 - Misfire Cylinder 3
P0304 - Misfire Cylinder 4
P0305 - Misfire Cylinder 5
P0306 - Misfire Cylinder 6
P0102 - Mass Air Flow
P0118 - Engine Coolant Temp Circuit High Input
P0491 - Secondary Air Injection Sys (Bank 1)
P0492 - Secondary Air Injection Sys (Bank 2)
P0421 - Warm Up Catalyst
P0171 - Sys too Lean
P0741 - Torque Converter

After i saw that all 6 cylinders were misfiring i decided to find out more before i picked up the plugs, that maybe there was something else causing them to misfire. I erased the codes with the CAN OBD 2&1 Tool and i noticed all the way home that the car idled better and even ran smoother. No idea. Has anyone else had this happen? And also can anyone give a hand in understanding some of these codes? Thanks in advance.

 

could be a maf o2 sensor combo.

Did you check the old spark plugs? Might even go as far to say head gasket if its as rough as you are making it sound. Ide pull the plugs and go from there.

 

Thanks. That was my next step. Any idea on those codes? Sys too lean means to much air in the air/gas mixture right?