2005 Audi A4 P0171 code

MEKNAAK

MEMBER
2005 AUDI A4
4 CYL
AWD
AUTOMATIC
86,000 MILES

Car keeps setting a p0171 code and p0507 code. Runs fine until warmed up-then idle will slowly go up to 1450 and then fall back to 800rpm. Has new plugs, fuel filter, and o2sensors. Has had throttle sync done. Smoke tested intake and pcv system and found no leaks. This is a 2.0 turbo with direct injection. When the idle acts up the short term fuel trim goes to 25 and then back to zero. The short term fuel trim also does this going down the road with no change in the way it drives. Help!

1 Reply

RASMATAZ

MECHANIC
75,992 POSTS

A lean fuel condition can be caused by:

* Low fuel pressure due to a weak pump or leaky fuel pressure regulator. (Use a fuel pressure gauge to check fuel pressure at idle)

* Dirty fuel injectors. (Try cleaning the injectors)

* Vacuum leaks at the intake manifold, vacuum hose connections or throttle body. (Use a vacuum gauge to check for low intake vacuum)

* Leaky EGR valve. (Check operation of EGR valve)

* Leaky PCV Valve or hose. (Check valve and hose connections)

* Dirty or defective Mass Airflow Sensor (MAF). (Try cleaning the MAF sensor wires or filament with aerosol electronics cleaner. Do NOT use anything else to clean the sensor, and do not touch the sensor wires)