Bank 1 too lean intermittently?

[cwilliamsws6]

Ever since I got my car 2 years ago this has been going on and it's always bugged me. My check engine light comes and goes a lot, sometimes it'll come on and go away after 5 minutes, sometimes it will stay on for days at a time, and there could be several weeks or even months that go by and it never comes on.

At one point I did have a vacuum leak that was so bad it would cause the engine to shut off when coming to a stop or turning slowly like into a parking spot for example. Remedied by replacing the vacuum line going from the intake manifold(??) to the power steering pump.

Only exhaust modification is when dumb 16-year-old me installed a Cherry Bomb glasspack. Catalytic converter is still OEM as far as I know, same with all sensors.

The car runs and drives fine, does not feel sluggish at all, my MPG is a bit low at 16 average maaaybe 20 mpg on a good day, but I also short-trip the car a lot because my drives to work and school both are ~1.5 miles.

The code I am getting intermittently still is P0171. It came on for about 20 minutes yesterday but this morning it was gone.

 

[BMWTurboDzl]

https://www.fixdapp.com/blog/p0171

 

[exranger06]

You need a scanner that can display live data, and look at fuel trims and o2 sensor data while holding the engine at various RPMs. A vacuum leak will have the engine running lean at idle and low RPMs. The lean condition would go away at higher RPMs, since there is little to no vacuum at high RPMs/wide open throttle.

If there is no lean condition at idle, then it's not a vacuum leak. If it's running lean at high load/high RPMs, then it might not be getting enough fuel. I would hook up a fuel pressure gauge at that point and see what the fuel pressure is.

 

[Audios]

My X3 had a head gasket problem, these exact symptoms. Barely consumed more coolant than normal also.

 

[javacontour]

Intermittent bad MAF or bad O2 sensor. MAF could be dirty enough to sometimes cause a lean code.

Intermittent vac leak causing unmetered air at times.

As others have suggested, you need live sensor data to see anything real time.

If you just want to fire the parts cannon, maybe clean the MAF and look at the O2 sensor.

That is pretty low MPG for such a small vehicle.

Without data, we are all guessing what to load in the parts cannon...

 

[cwilliamsws6]

Audios - come to think of it, I have had to top off my coolant a few times but not for a few months now.

javacontour - the MAF was replaced when I initially began chasing down the first vacuum leak issue before I figured out the one hose was cracked and basically collapsed in on itself.

 

[javacontour]

Just because you replaced it doesn't mean you didn't get a bad MAF or it's dirty. I can of MAF cleaner is cheap and worth a try.

A can of brake cleaner to hunt for vac leaks can't hurt either. Spray it around your intake to see if the engine speed changes while the additional fuel is sucked into the intake.

But has been indicated before, get some data. What is the MAF saying? How about the O2 sensors?