Seems mine just died, at least that is what my mechanic has determined and he is waiting to hear back on price of new or rebuilt one. Where can I find one rebuilt or new and how much should I expect to pay?
ECU failure on a Motronic spiders is not at all common. Some mechanics tend to blame expensive electronics when they feel too lazy to do proper troubleshooting. Unfortunately, the ECU is the most expensive component of the system and the wrong place to start if you want to start swapping parts.
If the proper diaganosis is indeed the ECU, I have a used one from a '91 that should work on your 90 spider.