Hi,

I have a 1997 Volvo 850 CD with 124,000kms on the clock.

Here's a bit of history.  The car started producing a
rattly/diesel-like engine sound whenever I accelerated.  Took it to the
mechanic who replaced the catalytic converter.  The old one was
breaking up apparently, and this solved the rattly/diesel-like engine
noise.  It was also at this time they discovered the oil was alarmingly
low (had not been topped up for 10000kms) - my fault for not realising
it consumed oil!  Then, went on a 4000km roundtrip and topped up 0.5L
of 15/40W Castrol oil every 500kms.  Car was great for most of the
trip, but by the time we got back, the car was very, very slow and
shaking when moving from stationary.  Once it got into about 2nd/3rd
gear, it drove fine.  Took it to the mechanic who discovered one of the
relays to the engine had gone, and after replacing that, the
acceleration has been back to normal.  Then had to change the timing
belt through regular wear and tear.

My problem now is that the fuel consumption has been, at least for the
18,000kms I have owned the car, very, VERY bad.  I had a previous post
on this, but just to recap, in 80% city driving, I am getting:

14.6L / 100km
16mpg (US gallons)
19.3mpg (Europe)

There has also been blue smoke coming from the exhaust only when
accelerating shortly after the engine has been idle for a minute or so.
This only started shortly after the timing belt change.  When at
cruising speed, there's no _noticeable_ smoke coming from the exhaust.

So this leads me to the question: Is my O2 sensor broken?  Is there
anything else likely to be causing the blue smoke and the poor fuel
economy?

Regards,

Han.