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Discussion Starter · #1 ·
I have been a fan of this site for 2 years now. I have been struggling with the Bank 1 & 2 too lean codes for over a year. Here's what I've done so far:

1. Replaced MAF sensor
2. Cleaned O2 sensor prior to Cat
3. Inspected all air intake hoses for cracks and leaks
4. Replaced fuel filter
5. Replaced crank case vent valve and associated tubing
6. Inspected DESA valve and resealed with RTV

(The Crank case vent tubing was badly dried and broke in my hand during removal.)

Now I only get the codes when driving on the highway > 15 miles. Around town, the codes will clear themselves. As soon as a drive 15 miles or so on the highway they come right back. ANY IDEAS WOULD BE GREATLY APPRECIATED!!!
 

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In all honesty those O2 sensors are due to be replaced at around 100,000 miles. You may get more miles out of them but they are no longer doing their job and gas mileage will suffer.
You may want to bite the bullet and replace all 4 if you have the time and resources.
 

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Not that I think it's related, but the DISA on a 330 does not need a gasket or sealant... Just an FYI. The gasket is built in to the DISA.
This is not correct. The DISA does indeed have a gasket that is removable and does go bad often. RTV won't seal it though, you need to buy a new gasket for it. Check German Auto Solutions. It could very well be the DISA causing the issue.
 

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This is not correct. The DISA does indeed have a gasket that is removable and does go bad often. RTV won't seal it though, you need to buy a new gasket for it. Check German Auto Solutions. It could very well be the DISA causing the issue.
Really!? When I replaced my DISA I didn't have to order any additional gaskets... It just came with one already integrated in the DISA body. I always thought the DISA for the 325 had a gasket or o ring that needed to be ordered separately. I've been wrong before though...

Sent from my PC36100 using Bimmer App
 

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Really!? When I replaced my DISA I didn't have to order any additional gaskets... It just came with one already integrated in the DISA body. I always thought the DISA for the 325 had a gasket or o ring that needed to be ordered separately. I've been wrong before though...

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Not integrated, already installed. There is a difference.

http://www.germanautosolutions.com/DISA_O-Rings.html
 

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My vote is a valve cover gasket or cracked valve cover. Both banks lean is a classic example of a vacuum leak. If you haven't done your VCG, just by a new valve cover (which includes gasket perimeter and spark plug gaskets) plus the VC fastener gaskets (15 of them for the M54) from your favorite OEM parts supplier.

I recommend replacing the valve cover because chances are you will crack it if you just replace the gasket alone.
 

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Of all the vacuum leaks I've found on my 2001 330, and there have been many, the most subtle was a vacuum plug on an unused nipple on the back of the intake manifold against the firewall. It had dried out and cracked, allowing air to leak in. To check this, you need to remove the panel that separates the brake system from the engine.
 

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Discussion Starter · #18 ·
New o2 sensors, valve cover gasket replaced. Now the strange part, driving around town, and short trips, the lean codes will clear. Every time I get on the highway for 15 miles or so, the lean codes return. Also, the car sat in the garage for three days and when it started up, the idle was very rough and I got two "misfire detected due to low fuel" codes. I drove a bock and the engine smoothed out and the misfire codes cleared. Any ideas?
 

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New o2 sensors, valve cover gasket replaced. Now the strange part, driving around town, and short trips, the lean codes will clear. Every time I get on the highway for 15 miles or so, the lean codes return. Also, the car sat in the garage for three days and when it started up, the idle was very rough and I got two "misfire detected due to low fuel" codes. I drove a bock and the engine smoothed out and the misfire codes cleared. Any ideas?
lean mixture codes can also be caused by lack of fuel. vacuum leak is most likely, but the fuel system is also something to take into consideration.

seeing that your car when idling runs just fine and gets the lean codes when driving high speed, did you check the vacuum line that goes to your fuel pressure regulator?

should do a smoke test to eliminate vacuum leak as a problem after checking that vacuum line. i've seen cars where a cracked valve cover is causing a vacuum leak, as well as a hole in the timing cover. smoke test will find these easily.

Of all the vacuum leaks I've found on my 2001 330, and there have been many, the most subtle was a vacuum plug on an unused nipple on the back of the intake manifold against the firewall. It had dried out and cracked, allowing air to leak in. To check this, you need to remove the panel that separates the brake system from the engine.
i just use light and mirror to check these :dunno:

This is not correct. The DISA does indeed have a gasket that is removable and does go bad often. RTV won't seal it though, you need to buy a new gasket for it. Check German Auto Solutions. It could very well be the DISA causing the issue.
maybe its just me but i've seen like 1 or 2 cars out of hundreds where the disa seal is the actual problem for a vacuum leak.
 

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If you have the tools and resources check the fuel pressure. I had the same code for quite some time and when I finally replaced my failing FP the codes cleared and never returned. The car had 140.000kms on the clock.
 
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