Hey Jason,
It figures that your car gives up the ghost as soon as you are ready to sell it...
I have a bunch of spare parts for my 924S including a good DME if you need it.
Checking the continuity between the DME and ref sensor would be a good place to start. There are a lot of invisible problems that can develop in 20+ year old wiring.
My multi-meter has become my best friend.... I figured out my throttle position sensor and MAF problem that way.
Next stop would be fuel supply - check pressure. A bad fuel pump or pressure regulator could be the problem.
www.clarks-garage.com
might have some good advice for you.
Hope this helps,
Brad