I've noticed this on the last few Rheem R90VA units I've serviced. The flame sensor doesn't stay steady at all.
Jumps from 0.5uA to 3.5uA to 7.5uA constantly back and forth. Anyone know why the new Rheem units do this?
I've upped a video of it in action
https://www.youtube.com/watch?v=oOD7CC3rvB8&list=UUvbUZKfy5gVw2BAczqZfItA