audijim113

2005 A8 basic with 4.2

For months I have been getting CEL P0171 and P0174 "Too lean banks". This occurs in the first 20 minutes or so after startup. I checked everywhere for vacuum leaks and even had a shop smoke test it. After I reset the CEL (with CARISTA) from smart phone. it does not appear again even if I drive for a hour or more. If I shut it off for even the time to go into a store and come back, the CEL is likely to be on again.

Other than the nuisance of the CEL, it runs fine and gets decent MPG on the highway. Local driving MPG seems worse than normal but hard to tell cause I do a mix of driving. My only indication is the trip computer. I know if is not really accurate but does provide an indication that something isn't right.

I took out the MAF sensor, cleaned with MAF cleaner, let it dry and reinstalled but the CEL keeps coming on.

I relpaced the complete MAF and now I am getting P0172 and P0175 "TOO RICH" It also seems to be running rough and MPG is down.

Is it necessary to do something like an adaptation or other setting if an MAF is replaced?

Any other suggestions?

MP4.2+6.0

Replaced with OE/OES parts? New? Other?

Yes, if you had...VCDS...you might run a throttle adaptation. Carista, no idea.

Two thoughts: 1. Try unplugging MAF and see how it runs. If it runs lousy, something else is up air/fuel wise. Look again for vacuum leaks, including broken manifold and such. 2. Big picture, what about basic tune up? How recent? Air filter and plugs that is.

audijim113

will try unplugging but regarding plugs and air filter - less than 5,000 miles ago.

Key point is the symptons changed from "too lean" to "too rich" after replacing MAF

Junius

What about fuel pump/fuel filter? About 5 months ago, I had a recurring check engine light that showed lean codes every so often. No symptoms otherwise. My mechanic checked the fuel pressure and the right fuel pump was giving slightly low pressure after startup. So went ahead and replaced that fuel pump along with the filter (which was old) and haven't had any codes since. Again didn't have any other symptoms other wise.

MP4.2+6.0

Got it. And again in turn, source of replaced MAF? New? used? Confirmed correct fit? Bosch/OES, or no name? As in, yes I would be suspicious of it. The unplugging often tells you something. If car either run smoother or hardly runs at all, it is telling you variously something may be wrong with MAF, or something may be wrong elsewhere.

audijim113

MAF was new, but a no-name one. Unplugging it didn't make a difference in how it ran. (This was at idle). I wasn't sure if you suggested driving it unplugged.

The only difference I notice was a slight clunk noise. I believe unplugging disconnected the air temp sensor signal, allowing the air door to move to cold start position to suck air off the exhaust when cold.

I don't have a VAG COM. The thing I check codes with is CARISTA, which is a cell phone app that connects to a WIFI thing plugged into OBDII. It's gives a bit more info than one of those plug in meters, which only give you a P-number.

MP4.2+6.0

Hard to know on MAF then without further diagnostics where you need VCDS type functionality.

A bit of trial and error without VCDS, but given your last reply and what was maybe an overlapping mention in the post starting the threat, also check the secondary air injection system. If it isn't working right, you get a CEL, typically with two cold-hot-cold engine cycles. If you are getting that CEL periodically, Make sure air pump is in fact turning on when you start car cold. You can feel pump running of you grab the motor body, and often sort of hear it if A/C (fan noise) is off. Can power it with 12V if you think it may be dead to check. BTDT. Can also be an issue with the combi valves which switch between the cold air injection function and the running temp EGR function.

Shamoye Lewis

check the plumbing between the MAF and TB a slight crack can cause you hours of unnecessary work..

if thats ok check the reading on the O2 sensor I'm sure the basic app can do this....