This car was obviously cared for over its whole life including a very recent dealer service. However, the plastic air intake tube from the air cleaner to the front grill was broken and then circled with duct tape! My first thought was that it was some one-year-only discontinued part, but it wasn’t. It was a $17 hose widely available at parts houses and dealers. This is no show car, but duct tape in the engine bay is below standards. 3 days later, problem solved. Also in the package were a couple of spark plugs. There was an intermittent miss on #1 and I decided to start my usual process of eliminating suspects. I pulled #1 and it was pretty black. I pulled an few more and they were new and light tan. I just changed #1 and the sputter was gone. The car now revved smoothly from idle. I am putting this down to a bad plug, but I will take a look at this new one in 100 miles.