While digging through a box, I found my scope probes.
I only had a few minutes before it was too dark to work, but I found it interesting to see a 300mV inverted spike on the 5v supply as well as the sensor return (sensor ground). The spike timing exactly matched and followed rpm. I also was able to see ripple from the alternator/rectifiers. Pulling B+ off the altenator eliminated ripple. The ripple increased when it was charging to about 100mV.

All this leads to a ground or loose wire so I will continue searching. I'll have a few days to make some decent probes to check at the ecm connection while the weather clears.

Of course when I had the scope on it it wouldn't act up.