Hi guys

My volvo s40 seems to have a cold start problem. It will start and run but you need to keep revving the engine or it will cut out. It goes like this for about 10-15 minutes, until it is properly warmed up, and then runs fine. It also smells like it is running rich. The EML light comes on but then switches itself off. The RAC diagnostic machine states an O2 sensor AND crankshaft sensor. As these are expensive, and there are 3 02 sensors apparrently, I was wondering if anybody recognised the symptons and could help. If so, I would be eternally grateful, love the car but if i replace all these parts, it will cost a fortune! Please help if you can. Thanks