After weeks of trying to solve my check engine light illumination, the mystery is solved. Codes from my Peake FCXII scan tool offered various aliments including a defective right side pre cat O2 sensor ($195). During the process of replacing my radiator I discovered a hose with a tee fitting running from the Fuel Tank Breather Valve to the base of the Throttle Housing assembly that had a deteriorated rubber cap (see attachment).
This deteriorated cap (item #7 Pt#11611727176 costing $.75) was allowing outside air into the system and causing the "Check Engine" light to come on. Perusing the related threads reveals this cap is often deteriorated or missing. My question is: What is the purpose of having a tee fitting there with a cap on it??? Happy ending is that my car is now running smoothly without "Check Engine" light for less than a dollar!

I believe the Tee-fitting is for other V8 model applications (maybe the E38??)

I think it's for hooking up a smoke machine to check for vacuum leaks. Ironically, most M60 & M62 cars probably have a rotten cap covering it, in effect, causing a vacuum leak!

This cap is pulled for smog tests (at least in Germany). The idea is to simulate an air leak and check the related components (O2 sensor) for proper functionality. Due to this artificial air leak the engine gets additional air which is not recognized via the MAF. Nevertheless the O2 sensor has to realize the additional air and correct the amount of fuel being injected.
As a matter of fact it is not just a cap but a little valve also called disturb.air valve.


Cheers
Wolf

This cap is pulled for smog tests (at least in Germany). The idea is to simulate an air leak and check the related components (O2 sensor) for proper functionality. Due to this artificial air leak the engine gets additional air which is not recognized via the MAF. Nevertheless the O2 sensor has to realize the additional air and correct the amount of fuel being injected.
As a matter of fact it is not just a cap but a little valve also called disturb.air valve. Cheers Wolf

Wolf,
Thanks for the clarification. One question. The cap that I purchased from BMW with the associated part number is a solid piece of rubber. How can this be classified as a valve? Regards, Whale

Lol :D Works great also to smoke your car. I found all sorts of interesting leaks when I blew smoke right into that valve. It made sourcing my vacuum leaks (aside from the obvious) real easy last year.

Wolf,
Thanks for the clarification. One question. The cap that I purchased from BMW with the associated part number is a solid piece of rubber. How can this be classified as a valve? Regards, Whale

Maybe they have changed it from a valve to a simple cap. The ones I know are small valves but this may have changed.

Wolf