Ok I drive a 96 328i, I have had a weird idle problem for a while now and have yet to figure it out. It's intermittent, when I first start my car, it doesn't want to idle, it's very rough, but if I rev the car over 2500rpm and slowly let off the throttle it will idle smoothly. When it is idling smooth, if I give a slight blip of the throttle it will then fall on it's face again and want to die. Also the other day I was driving down the highway and some idiot pulled out in front of me, so I had to slam on the brakes, but afterwards before accelerating again, my engine was about to die, I'm assuming the large vacuum drag from the booster caused it that time because it doesn't normally do that when I brake. Someone(BMW parts guy) told me it was possibly the Vanos because I have replaced the IAC and MAF and checked for vacuum leaks. Anyways, while checking the Vanos solenoid (which works when power is put to it) I decided to check the voltage supply to the solenoid. The positive lead is getting the 12v like it's supposed to, but the negative side, which is controlled by the ecu to control the solenoid, has a 4.5v POSITIVE supply. I am assuming my ecu is bad, I just wanted to get more opinions before I go spending all this money to replace it. I pulled the ecu out and apart, there was some corrosion on a few of the ecu pins, but that's it, the inside was immaculate, no burns, discoloration, or obvious swelling of any components.
And last but not least, no CEL.

So, any thoughts?

The symptoms you describe are a good match to any or a combination of; an intake leak, sticky ICV, or contaminated MAF. I'd certainly want to rule those out before considering the DME.

If the DME were to be bad, you should be seeing fault codes relating to the Vanos. The DME can tell if the Vanos doesn't shift when commanded to.

But what explains the positive voltage on the negative side of the solenoid? That's why I think the DME is bad unless there is something else that causes that.