[maximoline]

hey guys my car has a really rough idle and I've narrowed it down to either a bad MAF sensor or a vacuum leak. any way i could tell which one it is without doing the whole carb cleaner on all the possible leaks thing?

the codes i have are
P00BC
P0171
P0174

2007 BMW e92 328i

[relative4]

Smoke test.

[gbalthrop]

Originally Posted by maximoline

... my car has a really rough idle... the codes i have are: P00BC; P0171; P0174
2007 BMW e92 328i

Any work done under the hood recently by ANYONE, including Crankcase Vent Heater Recall?

If your Scan Tool will read Parameters (Most will ;-) read "Mass air flow rate" at idle (ALSO read RPM), and then again at 2,000 RPM with car stationary. Let us know what the values are. Here are the BMW Fault Code Lookup Definition for P00BC and Bentley Definitions for P0171 & P0174, AND links to the Fault Information sheets for P00BC & P0171 Bank 1 (P0174 Bank 2 has same information)
N52 | P00BC | 2D06 | DME: Air-mass system | MSV80
http://www.bmwfault.codes/XMLDiagVie...kANgAxADAANAA=

P0171 | 29EO | System Too Lean (Bank 1)
P0174 | 29E1 | System Too Lean (Bank 2)
http://www.bmwfault.codes/XMLDiagVie...EANgAyADAANAA=

As you appear to know, the function of the MAF Sensor is to meter/measure the mass of air passing the Sensor just behind the Air Filter Housing. The DME then provides the proper amount of fuel (stoichiometric ratio) to combine with that amount of air in the combustion chambers/ cylinders.

If UNMETERED air is entering the engine (air that has leaked into the air ducts/manifold downstream of the MAF Sensor), the DME fuels for the SMALLER amount of air passing the MAF Sensor and not the ADDITIONAL amount actually entering the engine (via the leak). That results in LEAN mixture on BOTH banks (P0171 & P0174).

If your MAF Sensor reading is too low for the indicated RPM at idle, but goes up by nearly the appropriate amount at 2,000 RPM, then your MAF Sensor is likely OK and you have a vacuum leak.

George

[320IN54]

I had this code on my 335i and I checked everything including injectors and o2 sensors. It turned out to be the MAP sensor. Try cleaning it first and see if it fixes it. If it doesnt just replace it. It's the cheapest part out of everything else so I would start there first. Idk about the N52 but it should be quite similar.