To start I have read every thread that has mentioned this code. My specific symptoms haven't been mentioned as a whole, I have chased the problem and thrown a few parts at it but would like to see if anyone has any insight.
A little history. 2001 330ci, 53,xxx when I purchased it four months ago, currently, 57,xxx. No issues were detected and the car ran perfectly for the first few weeks, SES first popped after about two weeks of driving. There were no obvious changes in the vehicle performance at first. Considering it was a garage queen the first thing I did was change the fuel filter and have the fuel system flushed.
The SES has been intermittent but the cycle of being on has gotten longer as time went on. This led me to think initially that it was an O2 sensor going bad since it would fault and then go back to normal on its own. Periodically the engine will start to run as if it's missing a cylinder, doesn't happen very often though. All I have to do is turn the engine off and back on and it runs normally again. Sometimes the idle will be a little rough but this is intermittent as well, usually happens prior to the "missing" symptom.
The fact that it's only one of the banks faulting led me to think that it wasn't a vacuum/air leak. I have all the usual suspect parts on the way as I type this. ICV grommet, DISA o-ring, SAI hose, both upper and lower intake boots, "F" connector and lots of vacuum line.
As of right now, both O2 sensors have been replaced and the MAF as well, no love.
If it was an air/vacuum leak wouldn't both banks be faulting or is it normal for only one side to fault?
I know this is beating a dead horse but any insight is much appreciated.
P0174 is a classic sign of vacuum leaks. At that age (yes, rubber and plastic parts wear with age) in betting there are several vacuum hoses that have a small leak. The ONLY way to find all leaks is to smoke test the intake. Try www.burms.org to find a shop that specializes in BMWs.
Does the DISA pass a vacuum check?
Ooops! www.bimrs.org.
Simple: Remove the DISA. Close the flap. Place your finger over the small hole. Release the flap. The flap should stay closed until you remove your finger. A small amount of movement in the flap is acceptable but no more than just a tad really.
Mine failed this test so it was replaced. Haven't seen a lean code since.
Thanks again!
If you're removing the DISA, you should also consider replacing the seal. Silicone o-rings are available and make sure that the DISA isn't an issue.
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That DISA valve is a pain. Given the age of your car, If it is original, it's probably bad. The diaphram usually gets weak, and cannot hold the valve.
The one thing I've noticed about these valves is that your car can still run okay with it being somewhat bad, as long as you don't have any other small issues that can throw the intake out of wack.
When I had this code, it was a combination of the DISA valve and and small hole in the intake hose.
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