Glad the idling problem was cleared up!
If you want to clean up somethoing else, go to the fuel vapour catch, the black cannister thing near the coil - mine was quite dirty, so removed it and cleaned out well with some brake cleaning fluid (takes 15 minutes all in and you feel good after
) Mine was Ok, but i have seen these completely clogged up with thick junk
Back to your problem: The S4's don't have this diagnostic button. L jetronics do.
Are you sure your lamda sonde is good? (the thing screwed in to the exaust pipe, just before your Kat)
What white block are you talking about. Here is a shot of my Motronic brain box, euro S4 so i presume identical to yours.....or is it out of shot? I seem to recall a white block under the back shelf which is connected to nothing, so I presume it is for a car perhaps with aircon, or auto transmission or airbag (built in for US market cars, and unused for us europeans!) or something like that.