I never knew there are 4 O2 sensors. To make sure I order the correct O2 sensor, the pre-cat is the one that connects to the manifold, right (number 1)?
thank you

I have had these 2 codes on SES for quite some time. Changed MAF to no avail. When in for service on other issues at BMW dealer, they tell me I have a coolant leak and valley pan needs replacement as well as valve gasket cover leaks that are causing my SES.

Does this sound right?

2001 X5 4.4i, 117000 miles
Plugs were replaced as well as hoses to oil seperator

Yes, but there are 2 pre-cats. The one on the front manifold is bank 1 pre-cat sensor (cylinders 1-3) and the one on the rear manifold is bank 2 pre-cat sensor (cylinders 4-6).

I found the problem. I popped up the hood to see if there are any air leaks and I just realized the oil cap is missing. A few days ago I had to add some oil but I forgot about the cap. I will use some duct tape until I receive a new cap.
thanks for your time guys

OK, I just replaced my MAF yesterday after getting codes P0171 and P0174. Drove it today after resetting the computer. Drove around for about 1 hour came back home and tested it again. Horray no P0171 or P0174 codes. I now have codes P1159 and P1161 which basically is telling me my MAF is bad. Now what?

Same thing here. Maybe Weasal 56 will give us some input. This is really frustrating.

For what it's worth, I (meaning my indie shop) replaced the big rubber boot and I got good results - for a bit. Then my mileage crept up again, the light came on, and I got the P0171/P0174.

Took it back, and they are now telling me that it's a leak through the "manifold tuning valve", which sounds to me like the Idle Control Valve. I let them keep it overnight to get it nice and cold and they used their smoker on it and found this item leaking, so they're replacing it and I'll report back on the results. I was about to get a MAF and replace it myself but I saw Greg's results...might still have to, but we'll see.

Thanks to all!

It looks like it was the item labeled #7 in this post - the "Adjuster Unit". The local dealer had 5 in stock, told my guys they go out a lot. $306 for the part, but it looks pretty easy to replace yourself and I'm sure you could get the part cheaper.

http://www.xoutpost.com/x5-e53-forum/...tml#post565171

Just drove 30 miles back to the office, no problems so far. Going to have to relearn how to drive without the code reader plugged in.

That (#7) in BMW terms is the "DISA flap" and controls the adjustable intake runner length system.

And for what it's worth, I almost never change MAF sensors at the dealer. Pretty much the only time I change them is when I read too rich at idle and the air flow reading is skewed from what it should be.

I've got the one they took out and I'm going to look at it tomorrow. The flap had become disconnected completely, and what they tell me is that air was being drawn in through the control box and entering the intake manifold where the shaft should have been. I've got all the parts - never heard of this happening but I guess it's possible.

That's all they changed, put on 100 miles since then and no SES, I'll check the codes in the morning just to be sure.