Hi Steve
Your problem could be a result of spooke rpm readings.
I have 3 possible "spooke" generators.
Try to move the fuel and gas solenoids to another position.
My tests shows that the solenoids should be placed as far away from rpm sensor as possible.
Another possible error is bad battery, it will also give you spooke readings on the rpm also, when low voltage.
Also check the fuel pump, and relocate pump as far away from rpm sensor as possible if necessaery.
Hope this will help you.

Regards
Anders Wikman