[A4] rear o2 sensor and lean fuel trim

[Stephen Lau]

My car's (2001 a4 1.8t quattro) check engine light came on and it 
was diagnosed at the shop (New Dimensions in Santa Clara, CA) as:
- Rear O2 Sensor - sporadic
- Long term fuel trim - too lean

I've read Andy's awesome post here
(http://forums.audiworld.com/vag/msgs/456.phtml), so now here's my
question...  could the rear O2 sensor being faulty contribute to 
the fuel trim being too lean? Andy's post seems to say "maybe". :)

Which should I try replacing first...the O2 sensor or the MAF? And
what's a good (cheap!) place to get them from.

I've never replaced either of these parts before, has anyone got
experience replacing these? Are they hard to get to?  Should I try
doing it myself, or just bring it back to a shop and have them do it?

cheers,
steve
-- 
stephen lau | steve at grommit.com | www.whacked.net | gpg 0x09E5CD21