dspur15

I have a 2003 Audi A4 Quattro 1.8 Turbo. My check engine light came on a couple days ago and I hooked up an OBD2 scanner to it and got a P0171 generic fault code and when I googled it all I could find was it meant that the MAF sensor detected too much oxygen in the exhaust but all the info I found seemed to only apply to 6-cylinders. Alot of people were talking about vacuum leaks and someone I know told me a vacuum leak would cause the car to idle rough. It seems like it is idling rather rough but I may just be imagining that because of paranoia. I'm definitely no mechanic so I was just wondering if anyone has any mechanical experience with fixing this or what the normal problem with this code is. Also would I have to find someone with a VAGCOM computer to turn the check engine light off. Thanks

lyleswk

One AZ forum thread calls out 3 potential issues: MAF (as you already note), a vacuum leak (as your friend notes), and fuel pressure and yes, it does apply to the 1.8t just like the 3.0. The thread talks to the l-shaped vacuum line that runs in between (not from) the coolant reservoir and intake runners. As for fuel, have you replaced your filter recently?

As for the CEL clearing, there is a potential that if the error is intermittent, it will clear by itself. There is specific criteria that is something like 3 full engine temperature cycles without the error reoccurring, and the light will go out. I know this has happened on mine. The other way to clear it is with VAGCOM, but again only if it is intermittent. If the error is permanent, the CEL will not go away.

Mitsum

For myself, got same problem with A4 20004 1.8T. First got code P0171 with rough idle. When cold throwing code P0507, and now it's throwing all P0300 codes. I did search for vacuum leak, nothing found. Cleaned the MAF, Re-fueled with injector cleaner. Found lots of fuel pressure at bleeder just before the injector. Today I'm gonna replace the O2 sensor (pre-calalyser). I also ordered a MAF. Don't know where to go after.
Pls help as well...

Mitsum

I also sprayed Quick Start spray around all the vacuum lines, no joy. Engine idle doesn't change at all.

lyleswk

What about fuel filter? You may get enough pressure, but not enough flow.

Mitsum

Wouldn't it run with problems other than idle. It only run rough at idle. I had plan to replace it, but haven't done it yet. If filter was clogged though, I think I would have hard time to accelerate. Am I wrong? I do lost some HP on acceleration, but it is smooth with no fault codes.

lyleswk

You would think so, but I have replaced fuel filters and cleared all sorts of different problems (noise, idle quality, accel, etc). It is pretty easy thing to eliminate and then go from there. by the way, you may not feel the "roughness" during an acceleration becuase of all the other noises and vibratons.

Mitsum

I'll order one, and I'll change it next week if problem isn't solve by then. Thanks for helping. I'll give you an update after the O2 sensor and after the MAF sensor as well.
I seen an other post talking about crankcase breather valve. Would this be possible? I'm getting more and more confuse as time go...

Mitsum

O2 sensor replaced, no joy... Run's a lot better when cold than hot, might run a bit too fast when cold, but no misfire. Trying to find something that would be affected by engine temperature, nothing comes in my mind. Just received the MAF as I speak.

Pete@ECSTuning

To the OP P0171 System too Lean may indicate a MAF issue, O2 sensor issue or fuel filter issue. The fuel filter can indeed affect things just at idle as if it is clogged fuel is not entering the engine at a low PSI but squeezes past debris in the system at higher PSI (more throttle). I would personally clean the MAF and change the fuel filter. Depending on abuse to the car and driving conditions 40k miles to 80k miles is a good service interval to change a filter at.

Now Mitsum, your issue seems slightly different. P0300 is multiple random misfires. If you've already cleaned your MAF you'll want to attempt changing your coolant temperature sensor. It helps control fuel trims in conjunction with you MAF. They are not hard to replace at all and are available here - click click.