I know I saw a thread explaining how to clean the MAF. Could anyone help me find that.

 

1.8tq 2004 a4- cylinders 1 & 3 missfire codes. I have changed all spark plugs. Coil packs were replaced not too long ago; although one looks dirty. I switched it to a different cylinder started the car & still getting same codes, same cylinders missfiring.
Also code P0171 - system too lean bank 1 code. Where is bank 1 and which CO2 sensor would this be most likely. I know where the upper sensor is. (left side of the engine extruding from the exhaust header.)
Help needed CEL is on but not flashing so I have a little more time. The stumbling/misfires seem to be getting strong.

 

Ok, that sounds like a vacuum/air leak, check all your hoses and check valves on and around your MAF, for cracked or rotted plastic pieces. If you find something replace it and if it doesn't fix your problem, replace your coilpcaks. Is that the only code you got?

 

I got codes...P0300, P0301, P0303, & P0171(system too lean bank 1) I ordered one new coil pack, it will be in tonight, and I'm going to switch it around. One of my check valves (upper left side one) is deteriorating but doesn't look that bad yet. I've been thinking about getting rid of all those. I checked all hoses and didn't find anything.

 

I would consider taking the time to just replace all of the PEM vacuum hoses. They tend to crack and deteriorate within a few years and with the braided covering you may never see the leak. My wife's 3.0 has a massive vacuum leak that I've been chasing and while I've been in there replacing the obviously bad hoses I keep finding more and more hoses with cracked ends that are makign my system leak. Determined to jsut do all of em and be done with it. I didn't hear any hissing at all until I started removing the top covers on the motor and really got in there...jiggling a few vacuum lines I suddenly got a few ends that were not connected and one check valve that snapped in two on me.

With the coilpacks. Rotate them all one cylinder, clear all the codes in the computer and go for a drive. If you get the same codes, its not the coilpack...if the problem moves one cylinder away, its the coil. Its important to clear the codes because you may have moved a bad coil to another cylinder and you're reading an old code in the computer now.

Bank 1 is the only bank you have...the 3.0 has a second bank.

Also don't discount things like a new ait filter, new fuel filter (people miss this all the time and it can eventually lead to pump failure), double check the gap on your plugs, etc. The O2 sensor might be bad, but you're much more likely to have a vacuum problem and thats cheap. I do not know which O2 sensor it would be more likely to cause this issue if it is an O2 sensor...but I'd bet it was the first one.

EDIT: Those codes indicate misfire on cylinders 1 AND 3. Did you happent o move your suspect coilpack from 1 to 3? If so then I bet it is a bad coil.

 

P0301 & p0303 is cylinders 1 & 3. I did switch around the coil packs and went for a drive, cleared the codes, and retested once the CEL came back; p301 & p302 are now showing. I put in a new coil pack on 3 so I'm replacing coil packs on 1 & 2. (Could always have a couple extra around I guess)
I'm sure the fuel filter needs cleaned so I'll do that this weekend any ways.
If it's a vacuum leak then would that be an audible hissing/ air leak noise?
Thanks for the advice everyone... any other suggestion are helpful.

 

On my car, one vacuum leak was audible...but I found two other hoses that were just rotted right off the connectors and just hanging there and there was no hissing at all from those locations. Its possible that the main leak I'm dealing with is at the root of the vacuum system so the rest of the system isn't pressurized properly, thus no sound. In all honesty, I'd say just make a single project out of it and just replace all of it wiht new hoses...otherwise you're jsut setting yourself up to have to chase one problem after another down the road.

 

P0300, P0301 and P0303 ARE the coil packs, change them all first and double check again.

 

You know kind of crazy... I changed only one coil pack that was dirty with oil residue in cylinder 1. Then I switched cyl. 2 &3's coil packs around to see if the code would change. It did not change, I was still getting the same codes 301 & 303. So I thought maybe it was deeper. I figured I would start attacking the Po171 (system too lean bank 1 code) and I headed for the parts store knowing from what I have read in forums it was most likely CO2 sensor or fuel filter. CO2 - $130 ish & then he looked up the fuel filter and it's not available because Audi manufactures a lifetime fuel filter on this car. Interesting, right? So he sells me this cleaner in an aluminum can called something like KB, GB, or KGB that is a CO2 / fuel injector cleaner. The misfire codes are gone and have been for 3-4 days now and the P0171 code was still there last night but today I am going to erase the code then wait and see if it comes back. Cross your fingers for me.

 

The P0171 is a vacuum leak, If you changed your coil packs and check for vacuum leaks then you can move on. I really don't think is your O2 sensor, good luck though.