Sqwawk 7500...this thread looks like it's been hijacked!

I can think of two things that might cause some exhaust smell in the
cabin:

(1) The plane's APU bleed air might be on and sucking in some engine
exhaust. But usually the APU bleed is only used for cabin ventilation
& pressurization on the ground, or sometimes during takeoff & initial
climb.

(2) More likely, the plane flew through the exhaust of another passing
jet and the a/c picked up the smell. The 717 doesn't recirculate cabin
air - it brings in fresh air for cabin ventilation and pressurization.
This also seems more likely since you describe it being an hour after
takeoff and short-lived.

As for the FO, did he visit the lav? Or maybe one of the flight
attendants told the crew that the cabin smelled, and he came back to
take a look (or sniff). I don't think running your hands along the
overheads as you move down the aisle has any particular significance.
But post-911 the flight attendants are noticeably more protective of
the cockpit area. I've even seen attendants block the area with their
body when a pilot comes out to visit the lav.