V8 Gearboxes & O2 Sensor

[Philip Ross <100423.1535@CompuServe.COM>]

Last month I posted a message to ask if anyone had any problems with V8
gearboxes.  One or two you of e-mailed me to ask me to post any info I received.
The only problem reported was a leak between the auto and front diff.  The
reason I asked about it is because our V8 has suffered gearbox failure twice in
50,000 miles and has also just had the gearbox removed for the third time in
order to have a leak from the diff fixed.

I find that the gearbox on our V8 is prone to sending heavy thuds through the
car.  For example if you are in 4 (e.g. at 50mph) and put the foot down just a
little so the car kicks into third and then lift off the box disengages with a
real thud.  Might this have more to do with the 4WD than the box itself?  Is
this the experience of others?

I have been interested to read all the comments about the 02 sensor and #5 fuse
on the V8.  I have just picked up our V8 from the main London Audi dealer with a
surging problem supposedly fixed by cleaning the throttle switch - however the
problem still exists.  When you are going along at a steady speed on the
motorway (say with the cruise control set at 90mph) you can feel the engine
pulsing as if the amount of fuel being supplied to the engine is being varied,
although the speed does not fluctuate.  You can also see the instant MPG jumping
up and down apparently in time with the pulsing of the engine.  I also find that
when accelerating in the car that it seems to go in bursts rather than a steady
rise in power and revs.

The London garage assured me that the O2 sensor was fine and that there was
nothing wrong with the car according to their computer.  I am not convinced the
O2 sensor is OK and suspect it is faulty causing the ECU to vary the amount of
fuel incorrectly.  Today I removed the #5 (O2 sensor) fuse for a few miles on
the motorway and the car did not drive any worse which suggests to me that the
O2 sensor must be faulty.  Am I right?  Is replacement the only option?  How
much are they?

Philip Ross
Edinburgh
Scotland.