Ok, well that makes sense as far as diagnostics go; what I meant was, don't assume anything -- just because something was working yesterday doesn't mean it's working today. A basic principle of troubleshooting is not to assume that something's working when you haven't verified it. But given the tach situation it sounds like you're on the right track.

Brad,

How much do you want for the DME? I took the car in to a shop and they seem convinced that the problem is in the DME, and suggested that I start looking for one unless I want to pay $500 for one from a junk yard.