VW Passat 1997 83,000 miles

For anyone reading this older original post and is experiencing a rough running engine or erratic engine speed behavior with DTC codes check your grounds first and clean them. Clean the battery terminals and all chassis ground wires (will be brown) before you do anything else. Older B4 Passats (1994-1998) all have this issue at some point and because the ECU is very sensitive to voltages throughout the individual sub-systems a sensed bad voltage will trigger certain behaviors like rough idle, engine speed suddenly dropping then increasing, you name it. You'll think your car is possesed but it's most likely a bad ground.