[ischmitz]

The common culprits are the DME relay and the FW sensors. Both have a tendency to fail. However, rather than replacing parts by probabilities I'd do some systematic tests.

The fact that the tachometer still registers when the engine doesn't make power and you coast with the car in gear does mean the DME is still powered (it's not an alarm or ignition switch issue) and the sensors are still reading the flywheel. This would indicate you either loose fuel (e.g. DME relay is intermittent and fuel pump shuts down, fuel pressure goes low), have too much fuel (O2 sensor is intermittently disconnecting) or you loose spark (damage inside the DME itself).

A DME relay is a cheap first investment. After that you'll need some diagnostics tools if you want to systematically track the issue down. And the fact that it is intermittent doesn't make it even harder.

Ingo