I have been having a terrible run with a 1997 V70XC Turbo. The check engine light has been coming on with a cooling sensor. I had that replaced today while the car was serviced. The light has come on again and my mechanic indicated the diagnostic message was "FET 232 - Long Term F/F Trim Idling". Having just repaired a main engine seal, replaced the turbo, the rear brake rotors, a MAF sensor and the coolant sensor I am not in the mood to part with further cash. I also wish I had visited this site earlier because I think a few of the recent bills could have been avoided.
Can anyone throw some light on how I could attack this one and if I need parts where to source them economically

Parts check out FCPGROTON they might be able to help you. http://www.fcpgroton.com

Long Term fuel trim Means a Vaccum leak some where or a bad Mass flow. And since you just had it replaced I dought it is the Mass Flow sensor.

My mechanic suggested the Oxygen sensors may need replacing. I believe there is one before the catalytic converter and one after. Do you think that is a possibility. If an air leak exists where do you suggest it is most likely

It could be a bad intake gasket. It could be a bad vaccum line/Cracked or have a hole.
I made a tool to connect to the induction hose to apply pressure to the crank case to look for vaccum leaks.
Some times the hose going to the turbo leaks at the Valve as well.

Thanks for your help. Also under the following link http://www.volvospeed.com/bay13.htm I was able to confirm what you suggested with pictures to guide. I will spend a couple of hours under this weekend to see if I can identify a leak, solve and reset.