84 vanagon. Symptons: running rich, very rich. Poor idle.

What i know: Somewhere in benlyey (24.36 or 36.24 ?) there is a trouble
shooting page. I did all those. The temp sensors were the exact same ohms
and were correct with temperatures (did it twice), oxygen sensor wire is
ok, oxygen sensor is less that 800 miles old, injectors were a lovely
pulsed conical spray pattern, afm is ok (track is clean and resistance is
per bentley), plug wires are ok, idle stabilizer ok, fuel pressure
regulator a bit high but this list said it was OK (no fuel coming out of
the vacuum side). That is about it. Didn't check the timing but haven't
messed with any timing stuff in years. I ran great then slowly got richer
and richer- most noticable on downhill stretches when i am coasting.

Would an oxygen sensor fail in a few months? Would a bad spark plug do
this (800 or less miles on bosch Pt plugs, wires, cap, rotor).

I am trying to not throw money at it, but trying to make intellegent
repairs.

What next? I guess i could replace the oxygen sensor with a cheap-o from
my local flaps (no place to get Bosch in town), do a compression check,
change the plugs at the same time.

There is a good mechanic in town that will be getting my business really
soon if i can't get her running.

Help!
TIA
Matthew

Matthew Pollard             http://www.uidaho.edu/~poll7356
Dept. of Chemistry               http://www.chem.uidaho.edu
University of Idaho                   http://www.uidaho.edu