[koziol]

Have another A8 in shop with P0174 and P0171,
did smoke test 3 times already no intake leak,
replace MAF sensor and did not help, after 2 days codes come back
and another strange thing is the engine accelerates up and down by itself
when it reaches around 2500rpm, below that and around 3000 rpm its fine.
have no idea where should I look now .

[rch11]

Have another A8 in shop with P0174 and P0171,
did smoke test 3 times already no intake leak,
replace MAF sensor and did not help, after 2 days codes come back
and another strange thing is the engine accelerates up and down by itself
when it reaches around 2500rpm, below that and around 3000 rpm its fine.
have no idea where should I look now .

Common Problems That Trigger the P0171 and P0174 Code
1.PCM software needs to be updated
2.Vacuum leaks (Intake Manifold Gaskets, vacuum hoses, PCV hoses, etc.)
3.Mass Airflow Sensor (MAF)
4.Plugged Fuel Filter or weak Fuel Pump
5.Plugged or dirty Fuel Injectors

[Clusters]

Engine surging up and down and a P0171/P0174 sure sounds like as vacuum leak. What does the freeze frame show for RPM? If the code set at or near idle, it,s most likely a vacuum leak.

Not familiar with this engine, but if the leak is in the valley and not external a smoke test won't show it well. If it has a PCV valve plug it off and the line to it, then plug the crankcase vent hose and put a vacuum gauge on the dipstick tube. If there is vacuum in the crankcase it is probably leaking into the valley.

One other place to look is the brake booster, plug the line to it and see if it improves. A smoke test won't reveal a leaking brake booster because of the one way vacuum valve.

[Ecmbuster]

Did you measure vacuum at the oil filler cap? What is the vacuum reading at the intake?
Do you have an internal vacuum leak?
Did you reset the faults and perform a throttle body adaptation?

[vwemporium]

Crimp off vacuum line zones to isolate at booster and N80 are very common.
Sometimes the booster leaks into car at pedal area.

[wirefan]

N80 faulty at own last car. equal symtoms to you. After replacing non error.