[ischmitz]

The fact that your issue is intermittent in my mind points to something electrical rather than a vacuum leak. In addition you say you get raw fuel. This indicates the DME is still seeing signals from the speed and reference sensor causing it to be in "run" condition. FYI, both the reference sensor and the speed sensor do fail intermittently the symptoms are different. It usually shows as cutout at certain RPM ranges and temperatures.

In your case something causes the mixture to go very rich. Two possibilities come to mind:

- The CHT is intermittently open and makes the DME think you'll have a stone-cold engine. The DME is then richening the mixture to the point where it is beyond being ignited. The result is raw unburned fuel.

- The engine is loosing spark intermittently (causing raw unburned fuel).

As others said check and verify the CHT is the later 2-wire version that doesn't rely on GND from its housing screwed into the head. If not replace it.

Next, you can measure its resistance with the engine cold (~ 2kOhm) and at operating temperature (~90 Ohm) and confirm its within spec. See the WSM for details. Keep in mind the issue being intermittent makes it hard to catch it in the act.

And then you could short it with a wire clip making the DME think the engine is fully warmed up and no enrichment is required. If that remedies the issue it strongly suggests CHT. However, with the CHT shorted cold starts will be extremely hard.

Next, the intermittently missing spark can be caused by a faulty DME. This requires inspection and potential repair of the DME.

Regards,
Ingo