My daughter's 2008 Passat comfort is having issues. First had P0303 DTC. Replaced the spark plugs and it didn't go away. changed the coil pack for #3 cylinder and it went away. P0304 DTC appeared, replaced the remaining 3 coil packs. The code will not go away. Car is running fine, does not stumble or hesitate anymore, but code keeps coming back. Found a TSB in regards to original problem but can't find any other info for fixing it. Can anyone help?