Three OBDII codes (running lean)
 

So I just scanned and reset my codes. I'm not sure if the software makes them appear is sequence or just by numerical order, but they were:

P0171
P0174
P0313

I'll check for the 1st code when the SES light comes back on. Luckily I have a can of MAF cleaner hanging around here, and I've never tried using this stuff before. Maybe I'll get lucky.


Otherwise the car runs pretty darn good when you give it some throttle. You can't sense a missfire when you mash the gas.

It could possibly be missfiring at low throttle, because I feel a little vibration/rumble which i suspected to be engine mounts. So more info to come. Until then, any ideas? Does anyone have a diagram of all vacuum hoses on the m54b30?

How's the fuel tank level? This seems like a recurring fault, so that's probably not the problem, but a low fuel level can cause a lean fault.
The first thing I'd check is the rubber boot which attaches to the throttle body. It tends to crack on the small portion that attaches to the idle control valve.
Do you have or can you get a fuel pressure gauge? I'd want to look at that next, but changing the fuel filter might be a good next step.

The fuel level never drops below 1/4 before filling up.

I will check the boot and any area between the AFM and intake manifold for cracks.

Do you know the location(s) of the fuel filter(s)? I remember the e30 has one that sits forward of the driver's side rear wheel. I wonder if it is in a similar location.

fuel filter is attached to the bottom of the car in a bracket behind a plastic shield. It's essentially under the driver's seat. The plastic shield is attached with a couple nuts, a couple screws, and a lot of the plastic expanding rivets. If you're careful, you can remove and reuse them.

So I let my tank level drop to below 1/4 and my SES light came back. I haven't read the codes yet, but assuming they are the same, do you think lower fuel levels can cause the engine to run lean? To me, that sounds like a weak fuel pump.

I'll get a fuel pressure gauge and test. Is there a specific type that is compatible with the m54?

I also like the idea of changing the fuel filter, inexpensive and a good starting point.

It could be a fuel pump problem. There's also a suction jet pump in the fuel tank that transfers fuel from one side of the tank to the other.

But I agree that the fuel filter would be the first thing to change. It's easier than changing the fuel pump.

I just did that last weekend on my 2001 530i. I didn't have any codes, but the mile to empty would drop very quickly when the fuel level low. I don't know it that problem is fixed, but it appears my fuel economy has improved.

My bet is Vacuum leak--one or more--search at the top of the page Vacuum leaks revisited--that will give you a list of places to start your seach for where unmetered air is entering the engine--

Poolman is right. You should check for vacuum leaks, because that's the most common source for lean condition codes. But if your fuel filter is original, I think you should replace it anyway.

I'd start here since I had the exact codes you have & it turned out to be simple after a year of on-and-off looking for the culprit:
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