[mehrlovin]

Hey All, need some assistance diagnosing a stubborn vacuum leak that is keeping my Bimmer in the garage since the emissions can't be passed on it.

Unfortunately a lot of work has been recently done so its hard to trace. 2007 E90 XI 100k

- VCG was replaced but it shows no signs of leakage and I think its ok
- Replaced Air Filter with a washable/permanent one and have heard some say it could be a problem.
- Replaced MAF in an effort to correct the unmetered air. I used a Amazon non-OEM part but I don't think its the issue
- Checked airbox, clamps and hoses for leaks but turned up nothing.
- Tried the old spray soapy water trick and it didnt work. Don't hear any air intake.
- Vacuum pump replaced - no affect.
- Resetting doesn't seem to help and it returns

Car runs normally and gets regular gas mileage so I think its a BS warning. Any tips? Should I get the Carly App to diagnose it?

TIA

[mousefarmer]

What does your code reader show? You have a code reader, right?

Why would you use a non OE mass air flow sensor? I've heard cars can be very picky about those things.

[mehrlovin]

I forgot the exact number but its the un metered air code.

[mehrlovin]

ECU
Code
Type
Status
Description
12
P00BC
PowerTrain
Confirmed
Manufacturer Defined
12
P0174
PowerTrain
Confirmed
System Too Lean
12
P0171
PowerTrain
Confirmed
System Too Lean
12
P0440
PowerTrain
Confirmed
Evaporative Emission System
12
P0171
PowerTrain
Pending
System Too Lean

Additional Information

PID
Description
Value
Units
SAE 0x21
Distance traveled while MIL is activated
0
miles

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[mousefarmer]

https://www.e90post.com/forums/showthread.php?t=678269

[mehrlovin]

That's a great threat but I have no whistling noise, the VCG and PCV are new as is the MAF. Injectors are cleaned up too. I may try to replace the MAF with a OE one and see if that works. I got a BAMPIC one which was cheaper but it should be ok.

[omadab]

Take it to a garage and have the do a smoke test. They send smoke through your system and wherever the leak is, you will see smoke coming out. Sometimes its something like a fuel injector... There's no way to find out.

You can also use propane and run it around the engine while its running and if the idle fluctuates, it gives you an idea of where it is.

Check your PCV hose for cracks, theyre known to crack overtime

[mehrlovin]

Yeah PCV hose is new from the VCG replacement and I did download the Torque lite app which actually shows the MAF is working and does register air properly. It goes up gently when I rev it too so it seems fairly normal. I did try a homebrew smoke test, and could not find anything. I cleared the codes and will be reinstalling the airbox just in case to see if that helps.

I may try the propane trick or use one of those long lighters. Thats a great suggestion.

[mehrlovin]

Tried operating the car with the MAF unplugged and the car turned off the first time. On restart, it sputtered for a while and then I turned it off. I am not sure what the benefit is of running the engine with the MAF off as it did not appear to offer any insight.

[mehrlovin]

Follow up on this thread now that the solution has been found. It looks like the part below from Amazon was in fact defective and after replacing the original bad MAF, I never had a good one to begin with.

This part generated two error codes. P00BC and P0174. I am reporting it to Amazon as I don't think this part works, like ever for a 2007 E90 with N51.

However, the part does generate ok data in the Torque app as well as Carly app. It reported Kg/hr numbers that were fairly normal (10-25).

I ended up getting a used, BMW OEM German made MAF from Ebay with a 1 year warranty. After clearing codes and doing 5 drive cycles, it has passed emissions and idles smoothly.

https://www.amazon.com/dp/B077W5G7S5...ing=UTF8&psc=1