So I just have a general question.. My 02 S60 2.4l at 155k,
When in park or at a stop light ( not moving ) the Rpm's flux from about 716-730's-780's and just do that over and over again till you drive.. you really cant notice it on the gauge, but I have a maxitrip installed and i just happened to click over to gauges and seen the rpm's moving a bit.. I was wondering if this is normal or should i watch out for horrible things to come from the ETM OR could this be a vacuum leak..

 

I had the same issue with my '02 2.4L n/a. Changed the front O2 sensor with an OEM Volvo replacement. No more hunting idle and better mileage.

 

I will have to keep that in mind.. Not sure i can get any better on the MPG I just drove from Edmonton, AB, Ca to Naples, FL and my AVG mpg was 31.3mpg..
I think good for the car.. am i wrong?

 

Could be a little better than that. My car is a non-turbo V70 and is probably a little less efficient than your S60 but on my Toronto to Orlando and back to Toronto trip I averaged 36 miles per Imperial Gallon or about 30 miles per US Gallon as per the display (I have a US car).
Typically the newer generation O2 sensors are good for about 100k miles. They are like spark plugs and need replacement as they become less efficient with mileage and will become slow to response.

 

Have the same car with a slight idle surge. My garage noticed it and referred me to the dealer who replaced the throttle control free of charge. Apparently there were so many problems with these that Volvo is extending the coverage of these to 10 years 200,000 miles!

 

Correction: They replaced my throttle body (Free) on an '02 with 103,000 miles.