Codes p0171 p0507
 

Have an '04 a4 1.8T Cabrio. Been getting the above codes for near a month. Spent 1450 at the dealer and another 1500 at a private "german" repair shop with no result. Can't seem to clear the codes and can't pass the smog test. Replaced pcv, brake booster, o2 sensor, MAF, suction, jet, 3 check valves, various hoses & clamps, coils, and plugs. Had three separate smoke tests- with last one negative. Ran injector cleaner through three tankfuls of gas. Engine runs strong as new. But still getting the two codes.

Anyone know of anything we've missed. Any suggestions would be greatly appreciated.

Not sure what smoke tests would cover but I would check intake gasket and vac lines, rough/high idle with p0171 code were caused by 3 vac leaks under intake manifold, removed manifold replaced hoses and such, did have some visible leakage around the intake gasket, replaced and runs well, was able to find the vac leaks using starter fluid, spray near any vac leak while engine is idling and youll get a small but noticeable spike in the rpms, p0507 is also telling you issue with high idle which could be vac leak or intake leak...