Looking up videos on troubleshooting a Bryant 373LAV flame sensor,
these guys clean it with a brand new five-dollar bill:
https://www.youtube.com/watch?featur...qL4lnk#t=13 0

This looks like a similar furnace to mine, with a similar issue,
and this guy does not recommend cleaning the flame sensor:
https://www.youtube.com/watch?featur...KsZhc0#t=36 6

After replacing the flame sensor, he shows the whole cycle:
https://www.youtube.com/watch?featur...KsZhc0#t=95 0

These guys use #0000 fine steel wool to clean the flame sensor:
https://www.youtube.com/watch?featur...gBB_R4#t=34 4
https://www.youtube.com/watch?featur...qlGfZv8Es#t=59

All say not to touch the sensor with fingers, which I didn't
know when I first had cleaned it.

But, interestingly, *all* (of those) simply clean or replace the flame sensor
without *any* of them testing it for the 5 or 6 uamps of control current.
(I'll google separately for videos *testing* the flame sensor circuit
but this is already long.)

Normally, I test things before replacing them, but, none of the
technicians in the youtube videos I've found bothered to test it
before replacing it.

Even so, I might buy a spare flame sensor and igniter, and keep
it next to the furnace. Any suggestions as to good suppliers?