My 91 850i has developed an issue that I am having trouble pinning down- it recently started to have a surging idle when warmed up. When the car is cold and I first start it it idles, runs, revs fine until the temp gauge is about 2/3rds of the way to the middle mark at which point the idle starts to surge back and forth between ~900 and 2000rpm.

If I unplug one of the MAFs the problem seems to go away- unplugging the other the idle surge still exists but is just slower to get to 2000rpm.

Any ideas?