Usually on those it can be one of the sensors or the harness - you got to pull intake manifold to get to either and there is really no good test if any of it is good: we replace both sensors and harness as a kit.
I got the tools to crown and thread the barrel - I would highly recommend finding a rifle that was already bubbarized, shoot, I got three to choose from if you need a project. I know that 91/30s are dime a dozen, but all I'm saying there a plenty reasonably priced "sporters" out there not to...