You need to prise off the plastic covers at either end of the front face of the potentiometer. They protect four screws which you can loosen to allow adjustment of the unit without removing it. I've just been messing with mine in a bid to sort out a rough idle and swapped it with a known good one. Turned out it wasn't the unit that was faulty but the two prongs inside were not making contact with the inner face of the pot. So, although the idle problem sees to have gone away (again) I suspect my Idle Control valve is faulty as I have been unable to make it move inside, even when applying current to the contacts. Anyone have any experience of testing these things?

As for replacing the pot, it is apparently available as a separate unit as a Bosch part, but not here in Indonesia where you would need to either buy secondhand or replace the entire air flow sensor unit. I've read in other forums that you can get the replacement part for $47 from Halsey Imports in the US, who apparently are only reachable by phone. I've got the info at home so if you need the part number let me know.

Good luck