I had this as well. I found the part pictured, sitting on top of my front bash "plate" (fabric). They almost missed finding the problem on mine also. Only low idle, usually in gear, fan engaged, sometimes with the wheel turned. Very annoying.
It was an isolator from the air box - which was...
Here's what I have been doing:
I bought a 6 ft cold weather block heater cord and ran it (loosely) from the heater plug to the passenger side front and through the drain.
When I am not using it, it is coiled up underneath the tremendous gap under the rear of the hood, passenger side...