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Discussion Starter #1
Hey all! Been a long time lurker, first time poster.

Just for background, I drive a 2005 330xi, and I bought it used about 7 months ago - currently has 260k km.

So I have a peculiar issue, and maybe some OBD2 expert on fuel trims can help me out. A few months back in the winter I had a lean condition on both banks 1 and 2. So I cleared that code and decided to deal with it later (lol).

This past week my CEL came on again - but to my surprise it was for running rich on both banks. I ran the live data on the fuel trims and both banks were sitting around -10%. This was weird to me as they were lean before, and the only thing that has changed is the outside air/temperature.

I decided to unplug and plug back-in the MAF. and Boom, back to running lean and both banks at 10%.

So this morning I did a live-data recording while driving to work which hopefully covers most conditions of driving (cold start, highway speed, warm idle, etc). I've attached the CSV to this post as a .TXT. You'll see from looking at it, that the short term fuel trims bounce ALL over the place. From as low as -20% to 30%. I'm completely at a loss for what could be causing this. The lean doesn't seem to improve when the RPMs increase - and there doesn't seem to be a method to the madness.

Does anyone have any ideas at all? My best guess would be a faulty MAF but I don't want to drop $200 on a new one if it's not the issue, if I'm unable to return it if it isn't. Also I've heard to stay away from the cheap Chinese knockoffs, and I'm sure that's mostly what I see on Amazon..

Work done so far (by me):
- upper radiator hose (2 weeks ago)
- coolant pump replace (2 weeks ago)
- coolant pump pulley replace (3 weeks ago)
- alternator replace (2 months ago)
- oil filter housing gasket (3 months ago)
- headlight ballasts (4 months ago)


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