I have a v40 1.8 xs 2000 model, I live in the UK and have the car at a non volvo garage, who can't find the problem either.
The car starts no problem but have to keep the revs high to keep it running, the enging management light stays on while doing this, as soon as the accelerater is released the engine stops it just will not idle. the garage say they are getting air flow error codes but have replaced air mass meter but still the problem can anyone help please.

 

2 things to have checked.
1. Make sure all fuses are good.If not then check the Induction hose it have a Valve in it that goea bad sometimes.
2. Remove the Idle motor and clean it out good and reinstall.