HELP ! ! !OBC Code (Code 1212) meaning

[Jazzman]

My '94 740iL suddenly lit up up the "Check Engine" light and started running a little rough, with the idle speed down to 400-500 RPM. :( It ran normal at speed but when you stop at idle it ran rough again. Then suddenly there is this noise that sounded like a wiped out bearing or a dragging belt, but everything looks normal in the engine bay. I pulled the OBC code and it gave me a code 1212. I do not have a Bentley yet so please help on how to fix this problem.

[micjordan]

Oxygen Sensor (secondary)

[shogun]

Lambda/O2 sensor no. 2. Can be a defective O2 sensor or a malfuntioning MAF.
See codes on Johan's page under miscellaneous links
http://shrubbery.student.utwente.nl/

[Jazzman]

the car runs rough at idle, around 400-550 RPM but runs fine at speed. At idle I have this unusual screeching noise like a seized bearing or a sticky belt , but disappears at higher RPM or when the car gets going. Also, after an engine shutdown and then a restart after a while, I get this smoke belch that disappears after driving off. It was only about six months ago that I have replaced both o2 sensors, the in-tank fuel pump and both fuel filters, so I know those are still good ...... or are they??? Thanks for any tips/info you can provide.

Lambda/O2 sensor no. 2. Can be a defective O2 sensor or a malfuntioning MAF.
See codes on Johan's page under miscellaneous links
http://shrubbery.student.utwente.nl/

[shogun]

It must not be absolutely the O2 sensor(s). It just says that the sensors give a wrong signal to the system. That means that the values are not in the permitted range. It could be a defective MAF or other things. Do you have any possibility to get a DIS diagnosis fault code reading at a dealer? This is much more detailed.

[BMWBig6]

I agree, unplug the MAF and see if the engine idles and runs better using its default programming. If it runs better, you found your culprit. A bad MAF will often return O2 sensor errors since the engine's air-fuel ratio cannot be dialed in properly and the sensors become covered with soot. Catching the problem early will save the sensors (which will return to normal operation after a few drives), but if you wait too long, the sensors will be ruined (costing another couple hundred dollars).

[Jazzman]

Guys, this afternoon i started it and ran it for a few minutes and then try to remove the oil filler cap. The idea was presented to me that I should have a HUGE vacuum from the filler neck, and if I have pressure instead then the culprit is most robably the PCV plate behind the intake manifold (which also might explain the smoke from the tailpipe after a restart). I took the cap off and just to twist it open is tough because of the big vacuum, so that shot down the PCV theory. But then as the engine again is idling rough with the screeching sound with it, I pulled the plug off the MAF sensor and the idle smoothed out to almost normal, WITH NO SCREECHING sound. As soon as I plug the sensor back the symptoms again showed up. Now does that confirms the possible bad MAF sensor?

[BMWBig6]

That's a pretty good indication it's the MAF, but it would be nice to see a MAF code come up in addition to 02 sensor codes (mine yielded both error codes, but not 100% every time). If you have access to another MAF, you could try swapping one in to see if it holds the idle and runs like new. Otherwise they run around $100-200 used from salvage yards, and almost $400 new from the dealer. I bit the bullet and bought a new one, since I don't want to take chances on another old MAF.

[shogun]

So it is the MAF

BMWBig6 had the same problem and he replaced the MAF and all was solved. Do you have any possibility to get a used one? They are quite expensive but often available on Ebay or from used parts dealers.
As for the price check at
http://www.bavauto.com
Here is a link to check the MAF
http://shrubbery.student.utwente.nl/sean750/MAF_v12/MAFtroubleshooting.htm