Throttle Nut Torque?

Have been chasing imprecise throttle control for months... thought I had it solved, but over the weekend it popped up again. Decided to take a closer look, and believe I've found the gremlin. The problem is that I'm not sure the proper way to address it.

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The nut (green arrow) is slightly loose, allowing play in the linkage. I can easily tighten it, but TOO tight seems to bind up the butterfly. What's the proper torque or procedure?

Also, I've noted that the keeper flap (yellow arrow) isn't flat against the nut to keep it from turning. I assume it should be bent into place once the nut is tight, yes?

Thanks

 

Thanks, Mike. That's how I've done it on other cars, but wanted to make sure this flat tab wasn't some weird Italian thing.