From the diagram, I'd say #2, but that'd be an educated guess...again, post cat sensor, so that's the only one...and that's assuming that's your issue...which does seem likely.
I'd wait for confirmation from someone who isn't guessing, just to be safe!
I'm so depressed. No one wants to come see me in NYC: Sat, Oct. 8, 6 p.m. at Greenwich Village Comedy Club.
Mangofy your E46!