YES!!
Missoula to Lewiston on Hwy 12 is my favorite ride. Great little "town" Lowell, Idaho. A gas station and a diner. Best food in the US at that diner, Wilderness Café.

Hell's Canyon area, great place to stay is Baker City (think it's just called Baker now) Lots of great roads out of there. Hells Canyon Motorcycle Rally is July 11 - 15 if that's in your timeframe. Registration started Jan 1, google it and order a package. You'll get shirt and route maps and wrist band for entry in events. The route maps are worth it even if you can't be there for the Rally as they show all the best routes. During the rally, you ride a route take a photo at the designated spot and when you get back into Baker go to registration tent, show the photo and you'll get a pin for that route. I think there are 8 to 10 pins/routes in all.

If you're going to be there during the rally, hotels can be scarce, get reservations now.

I'll be there again this year. If you're going to be there during the rally hit me up.

EDIT: Reread your post and saw you were planning your trip for Sept. So all the rally info was unneeded. But be sure to hit up The Bearded Dog in Baker. The old man will tell you some great riding routes.

 

In Baker, the big brew pub is Barley Browns, good food good beer. But ask around for the Bearded Dog, it's on a little side street. It's more a growler fill, but there's a little bar with 6 or 7 seats and about 20 local (Oregon, Idaho and Washington) beers on tap. It's owned and run by a crusty old biker guy. He's got lots of great stories, and he'll tell you great places to ride if you didn't buy the rally package with maps. In fact, first year I was there he had extra maps under the counter and gave us a couple (it was the week after the rally)

Cheap and strong mixed drinks at the VFW and music and dancing on weekends, you don't have to be a member, it's about 2 blocks from The Bearded Dog.