OK, I must post now after searching the forums and trying various things.

I just bought a 2001 X5 3.0 with 70K miles. It runs great. I Live in the city and get about 14.5 miles to the gallon. I should also tell you that the car sat at the bmw dealership for 2 years before I bought it from them. So, in the past 2 years it has only been driven about 35 miles.

After driving it for about 1000 miles I got the ses light. I found that it was for the P0174 and P0172. It goes on and off. It doesn't stay on all the time. Here is what I have done already:

1.) Checked for any air leaks in the hoses. I have looked in all the areas they usually are according to this awesome forum and other places and nothing.

2.) There was a K&N filter installed. I read that they might be bad for your engine and bad for your MAF sensor so I bought a paper filter and took the K&N out.

Today my girlfriend (that drives it the most) told me that it usually comes on when it gets to a quarter tank of fuel left. I find that odd but...?

So, I went to go fill it up with 93 octane and included a fuel cleaner/additive, start up the car, and no ses light!?!?!

What do you think? Maybe O2 sensor? Any correlation with the ses light and a quarter tank? Maybe the fuel pump/filter?