picasso xsara diesel 2004. 2 litre hdi engine fault light. ?

Hi. The Picasso engine warning light came on again today . Did it the first time a month ago. Then turned off and was fine. She. It comes on... it runs still but with low revs and loss of power. Then is fine again abs thr orange light turns off. The swing arm is being changed tomorrow but I doubt it's anything to do with that. Do you think a good service would sort it or do I have to start saving money I don't have for a new car ??