I'm somewhat of a rookie... how can I check if the O2 sensor is functioning correctly..... if it wasn't, wouldn't the check engine light come on at least periodically?... it doesn't.

I've given up on the air pump... the lines running from it are corroded and the adjustment/mounting bolts are seized. I probably could fight for another 2 hours to get them off, but I don't really see the point, given it's limited value.

I replaced a few vacuum lines today which were brittle.... almost like macaroni. Didn't notice any audible or visual difference afterwards but who knows....