ECU replacement 1994 325 is
My 94 325is has a problem. The ECU apparently has a problem according to a local mechanic. The problem manifests itself as trouble starting and the engine suddenly stopping while running. In a failed state, it was taken to the mechanic who managed to get it running again by giving the ECU a whack. The mechanic suspects some faulty soldering points inside the box. This is a high millage car (~200k) but I do not want to get rid of it yet. In fact, it runs pretty good when it's not suddenly dying on me. Cosmetically, it looks pretty good, too. However, the price tag for replacing the ECU is rather high, about $750 for a new one plus labor. This is a lot of money for me. I have been keeping it running by leaving the panel loose and giving it a whack as needed, but this gets really annoying. I have been thinking about replacing it myself, and I have seen on eBay that replacements can be bought for <$200. Also, looking at the ECU in the car, it looks like replacing it is as simple as loosening some screws and plugging in the wiring harness, though this might be wishful thinking. My questions:
1) How picky is the car about the ECU installed? For example, does it have to be an ECU out of another 94 325is, or will any E36 ECU do?
2) How difficult is the installation?
3) Are there software issues to be considered?