And maybe I skipped it, but have you cleaned the idle valve? Also I had a weird idle when i first got the car. It was a green vacuum line with a yellow stripe that connected to a short rubber tube just under the front of the intake and behind the dist. A couple lines run that way. Maybe it was a repair, but it has come undone a couple times. When I have an issue, its the first thing I check.

__________________
1991 560 SEL / 185k miles
1992 750il / 17k miles - project car