I run digifant engine management for my inline VW ABA Jetta motored
vanagon...same as the stock Vanagons but with the inline motor providing
the go..A few weeks ago I had some problems with my engine management
system and traced it to a dysfunctional Oxygen sensor.    I'm almost
positive the problems were a result of bad wiring between the O2 sensor and
the ECU, but I have no actual confirmation of that.

   Anyhow, I was unhappy with the cost of replacing the Bosch 3-wire heated
Oxygen sensor in my rig...the best I could find was about $70 for another
Bosch heated sensor, and  that one didn't even have the proper plug for my
wiring harness...So I did some research, called around a bit and
asked...and the general response was that I could replace that 3 wire
heated oxygen sensor with the single wire Bosch sensor and save myself
about $50 without any real downside to engine performance.  But......No one
would actually come right out and tell me that.   Lotta "Oh, that should be
OKs"...and "I don't see any reason why that wouldn't work fine"s....There
was also some nebulous opinion as to how to properly connect the
sensor...Should the shielded wire loom carry a grounding connection or
not...etc...

   Anyhow I bought a single wire Bosch from Van Cafe and installed it.
The results are quite satisfactory.   The only downside has been that after
sustained highway driving if you shut off the motor for a short while the
idle speed is a little low...low enough to stall sometimes...for just a
couple of seconds, until the O2 sensor gathers enough heat to resume proper
function, I guess.

   I have regained my fuel economy...back up to 24.xx mpg after 3000 miles
with the new sensor. the O2 sensor i again modulating the fuel mix
properly....When running with the O2 sensor disconnected from the ECU, I
was seeing around 4-6mpg less gas mileage but the motor felt quite happy
and strong..

   So, in my case, I successfully saved some money on that part and gained
back my good gas mileage.   Here's a handy app to help you track your
fuel...there's one for the smart phones, too....
http://www.fuelly.com/dashboard