too lean fault code

[camfambmw540]

car = 99' 540iA

My idle is too low, around 450 rmp, car occasionally dies. OBD error codes indicate too lean right bank and too lean left bank.

My car runs as well as the day I brought it, no other problems, 80k miles, any suggestions on what could be causing this???

Thanks guys.

John

[Jared at Pelican Parts]

Could be the O2 sensors. Have you done any work to the enigne at all?

[camfambmw540]

no, nothing but standard maintenance. Wouldn't the OBD II code indicate a fault in the O2 sensors? A friend of mine said it might be the mass air flow sensor too. How would I know without paying out the ying-yang at a dealer or needlessly replacing parts?

[Jared at Pelican Parts]

How did you detemrin it was running lean?

[camfambmw540]

I plugged a OBD II scanner into my OBD II port to the left of my stearing column. It game me 2 fault codes: 1 = P0171 and 2 = P0174.

In the manual for the scanner, it states that these codes are "Lean left bank" and "Lean right bank" respectively.

[RickPA]

Sounds like it could be an intake manifold leak. On some Ford's a cracked lower intake mainfold gasket caused the same codes.

[Jared at Pelican Parts]

I would agree, if it's not O2 sensors, it's most likely a leak. Check your vacuum lines.

[camfambmw540]

I might be sounding like an idiot here, but, the only other car I work on is a 78' Trans-Am (35k miles on it, my first nice car, picked up when I was a kid), on it, I just hook a vacuum gauge up to my manifold line and read.... that simple. Question, is there a easy way to test for vacuum leaks on a 99' 540i, what should the vacuum be, does it differ depending on where I hook a gauge up, etc....

If you could point me to a web site or a prior post, I would greatly appreciate it.

thanks

[camfambmw540]

How do I know if it is the O2 sensors without replacing them?????

thanks

[Jared at Pelican Parts]

If you send me your email address, ill send you an article on how to test the sensors

[Bob540iA]

Here are a couple links that may help.
http://www.bmwe34.net/e34main/trouble/engine_diagnose.htm
For info on vacuum testing.

http://www.mr2.com/TEXT/O2_Sensor.html
For info on testing oxygen sensors

[camfambmw540]

Just to let everyone know, it was my Mass air flow meter. I hooked up my palm pilot to my OBD II port, ran "live" for about 50 miles, graphed out the Mass air flow vs rpm and MAF vs Fuel trim (right and left) and it indicated (at least that is what I thought) that it was not the O2 sensors, or, if it was, coincidently, they both failed at the same time. I was right, problem solved.

John