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gomi_otaku, Technician
Category: Audi
Satisfied Customers: 3462
Experience:  VW certified technician, Chicago VW/Audi Training Center, Seattle VW/Audi Academy
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2006 audi a4 2.0T, have had a P0171 lean on idle code i have

Customer Question

2006 audi a4 2.0T , have had a P0171 lean on idle code i have been chasing , replaced PCV , O2 sensor ond purge valve with no luck . Am thinking the intake runner flap is damaged / dislodged from the intake and recently P0507 is activated as well with an increased idle which backs up my theory . Rough idle now as well on cold start up . Can you back this up
Submitted: 1 year ago.
Category: Audi
Expert:  gomi_otaku replied 1 year ago.

Judging by the fault, and the rough idle, I would say you have an intake air leak, not a bad sensor of any kind. What scan tool are you using?

You replaced the PCV on the front of the valve cover, correct? And if you try to remove the oil cap while the engine is running, you can remove it OK, it doesn't suck down tight and unable to move?

Customer: replied 1 year ago.
PCV is on the top/side on the valve cover near the centre of the intake manifold and yes it was replaced , oil cap easily removed .
Customer: replied 1 year ago.
using VCDS
Customer: replied 1 year ago.
Expert:  gomi_otaku replied 1 year ago.

The intake flap should not affect the lean reading, no matter what position the flap is in, unless there is actually damage that results in an intake air leak. Have you checked the adaptation values for idle and of idle? If it is over 7% at idle (and especially if it is in the high teens) then you need a new MAF

Customer: replied 1 year ago.
Adaptation values at idle ? Are you talking about fuel trims or actual maf values , if maf what is the measuring block number . Did the wide open throttle maf test and it showed around 165- 170 which is about the 80 range specified
Expert:  gomi_otaku replied 1 year ago.

correct, the fuel trims, MVB 32.

Customer: replied 1 year ago.
They looked ok I wll check again tonite after work , it's idling up around 1400 with nothing on , idles normal with a/c on
Expert:  gomi_otaku replied 1 year ago.

I noted you said that it idles rough on cold start- does it clear out after a little while? It may be that you are having an issue with carbon fouling on the intake valves. This is pretty common, and then when you cold start all the fuel gets absorbed by this carbon so it runs lean until it can get fueled correctly. If you have a borescope with a 90 degree view you can look down the spark plug holes, or if you have a straight borescope you can take the manifold pressure sensor out and go straight down one of the runners. otherwise you would have to remove the intake (which you would have to do to clean these anyway)

Customer: replied 1 year ago.
Long term ft is about 8 % short is floating around 0 running in closed loop
Expert:  gomi_otaku replied 1 year ago.

ok, from those readings I would not suspect a MAF, or an intake air leak, or it would be adjusting like crazy to account for extra air.

Customer: replied 1 year ago.
I think I was reading the short-term and long-term too soon after resetting the engine code short term is reading about 16 and the long term is reading about 13
Expert:  gomi_otaku replied 1 year ago.

did you ever get around to replacing the intake, if it is actually damaged? Or can you hear air sucking or whistling around the intake area with the engine running? I would expect with fuel calculations like that after a while, you either have a leak that you should be able to hear, or you have a bad MAF.

Customer: replied 1 year ago.
I did the full throttle pull while trending the maf reading and it reading was around 160-170 so I think it's ok , I have the intake off now but also have to work at real job , stay tuned