Poor idle, low fuel efficiency, and engine misfire codes are all symptoms of worn spark plugs and/or coil packs. Replace yours with Genuine parts from Audi to get your engine running as well as possible. This is especially important with modified engines that require maximum spark to maintain maximum performance.
Coilpacks - Set of 8 - Genuine Audi Delphi (077905115T)
Spark Plugs - Set of 8 - NGK (BKR6EQUP)