If the fuel filter on your car hasn't been changed in a while, you may want to add it to the list of things to replace.

"i'm also collecting web sites for parts (new and used)."

I doubt that one souce will have the best price on everything, so here are some places to compare for new and used parts:

NEW PARTS:

http://www.rprusa.com/

http://www.importpartsspec.com/

http://www.gapa.com/

http://www.nilssefeldtvolvo.com/

http://www.borton.com/parts.html

http://www.fcpgroton.com/volvo.htm

http://www.cybertroll.com/

USED PARTS:

http://members.home.net/stevekafasis/

http://www.volvousedparts.com/

I have not done the throttle body myself, but recently had my Volvo mechanic do it to my 89 244. It made a big difference in the performance, it now purrs like a kitten at idle- smooth as new. He did completely remove the TB from the car to soak it in carb cleaner, and also replaced the gasket. Check the 700/900 FAQ (same engine/TB as 240), there is a good description of what you need to do there. I would not replace the O2 sensor if the check engine light is not on. That is a part that is either good or bad with no in between, so it does not make sense to replace it (can cost up to $150)if it is working. If you want to improve gas mileage and performance do a complete tune up if you have not already- i.e. replace spark plugs, spark plug wires, distributor cap, rotor, air filter, change oil, etc. Be sure to use OEM parts or OEM Brand parts (ipdusa.com is a good source). I had a problem with my car because I used aftermarket parts and had to go back and replace everything 3 months later. Another way to improve gas mileage- check the air in your tires, should be 35 psi cold.