I have an 86 325, and it has a very similar problem, but it also has a few more. Sometimes, when the car is cranked, the rpms go up to around 1500 and the brake lining dash light comes on for a second, then it goes off and the car begins to idle normally.
The car also stalls, but only in a few ways, and I can crank it back up immediately, though I have to turn and hold the ignition for a few seconds. When I first start the car, if I reverse and apply any gas at all, the car stalls. If I come to a stop too quickly after starting, the car stalls. After the car has been running at speeds around 30 to 45 mph for a few seconds without having to stop, the stalling problems seem to go away. I have noticed that when the car stalls, it starts shaking, and the battery light begins flickering until both the battery and oil lights light up, but the power stays on.
On an unrelated note, the radio is very buggy. To get sound from it I have to play with the volume knob until sound comes from all of the speakers. Any help with this?
My car has similar symptoms, Ben, but I haven't found a fix yet.