Hello Sir,
naalala ko lang erpats ko nong nagkaron sya ng problem sa A6 nya, parang ganyan ang naging issue, nilinisan lang ang MAF sensor, then OK na... But I'm not saying na yan ang sira, just try to test some of the items listed below...goodluck

17544 P1136 Long Term Fuel Trim Add.Fuel,Bank1 System too Lean
http://www.bentleypublishers.com/tec....dtc.table.htm
17544 P1136 Long Term Fuel Trim Add.Fuel,Bank1 System too Lean
17545 P1137 Long Term Fuel Trim Add.Fuel,Bank1 System too Rich
2 different codes#
if its rich, then it may be a vac leak
if its lean then it may be clogged injectors
*17544/P1136/004406 - Fuel Trim: Bank 1 (Add): System too Lean *
Possible Solutions
Check Mass Air Flow (MAF) Sensor
Check Fuel Pressure Regulator
Check Fuel Pump
Check Intake/Exhaust System for Leaks
Check Secondary Air Injection for Leaks
Check Vacuum Lines for Leaks