P0171, P0174 resolved

[NoDef]

Hi Everyone,

About 4 weeks ago, my service engine soon light came on (2003 X5 3.0i). I had the codes read and found P0171, P0174 indicating both banks were lean. Anyone who has had to do the search for these codes knows there are many reasons and lots of things to try. In my case it was a failed DISA valve which was causing a vacuum leak. As is always the case, this was the last thing I tried in a long list of replacement parts. In any case, I wanted to give some details which I would have loved to have found when I did my initial search. Here is what I did:

1) I purchased a CarChip to read the engine codes and reset the SES light. For those of you who haven't seen this device, its an OBDII code reader which plugs into the port and monitors on a 5 sec interval storing a variety of engine information. This was useful not only to reset the codes, but also to see the readings from the O2 sensors and the lean condition on the fuel trim.

2) I searched for vacuum leaks. Apparently the most common location for this problem is the elbow just after the MAF sensor. Mine checked out fine, and I didn't hear any vacuum whistle.

3) I cleaned and eventually replaced my MAF sensor. I didn't see much of a change after cleaning, but it was clear that the engine ran smoother when the MAF was disconnected. So I decided to bite the bullet and replace the MAF. I bought a new Siemens OEM replacement from RAeuropean (http://www.rmeuropean.com/). SES light remained.

4) I replaced the fuel filter. There are several good DIY on the net for this. My only trouble was removing the fuel lines, for my X5 (2003) they had a couple of slip on connectors with green clamps to keep the connectors from slipping off. There were no hose clamps. SES light remained, although between this and the MAF I think I picked up 1-2 MPG.

5) After a more exhaustive search for a vacuum leak, I heard a whistle from the DISA valve (also called the adjuster unit:11617544806). After a more extensive web search, I realized I should have checked this first. It is easy to remove, just 2 T40 torx bolts, then it pulls out from the manifold. When you pull it out, you should see a valve.
In my case, the valve was only connected to the box on one side, the lower pivot point had broken entirely. This allowed air to enter the manifold (after the MAF) - apparently this is not uncommon. In fact the original part number up to 04/2004 has been retired. After a short trip to the dealer (and ~$212) I was back in business with no SES light. I also watched the long term trim readjust with driving (using the CarChip). After a couple of hours of driving, the long term had decreased considerably.

In the end, I'm happy that I replaced the MAF, Fuel Filter, Air Filter, and I even did a set of plugs as I am now just over 105,000, so many of these lifetime elements are probably close to EOL. I also saw a jump in MPG.

I hope this might help someone else when confronted with these lean codes...If I were to do things over, I would first check for leaks (5 minute job), then pull the DISA (10 minute job), then clean/replace the MAF (15 minute job), and only as a last resort work on the fuel filter (2 hr job).