Even though the tacho is bouncing around, the other gauges seem to be fine
through it all. Again, the rpm's don't really change, just the tacho.
I have myself suspected the coil or wires connected to it. I have not been
able to make the problem come or go by wiggling wires. Which I have
inspected but they all look solid. That's not to say it's not a wire on
connection. I guess I could replace all the connectors just in case.

Am I right in thinking that the FALSE change in rpm is tricking the EC into
changing fuel management or timing, which is causing the change in
performance? If so, wouldn't this limit the cause of the problem to the
engine compartment?

Any other thoughts on this or the oil light/buzzer thing?