Just found your site. It's great. I use one for my 325i and it is the best friend that a diy mechanic ever had. My new problem is my girlfriend's 99 320.
She has followed the dealer service schedule to the letter. All work ( even new tires ) performed by local dealer. At the 100k mark she had a service engine light come on. Dealer says "no problem, we can't find a code"
Next service @ 106k , light still on. Dealer says "no problem, no code, we changed the air filter"
Next service @ 112k , light still on. Dealer says "you have a problem, You need either a mass air sensor or an O2 sensor, I can
not tell which" Price estimate equals $ 1200 cdn.
My questions are:
Common Problem ?
Anyone know of any service bulletins or hidden warranties ?
Can I replace it myself ?
Where would you suggest I shop for the part ?

Thanks in advance for your help on this.