How can I fix My Renault Megane 1.4 16V Liberte Year 2000 model?

Hi. I have just been given this car by my mother with a full service history. It has worked fine until last night when it started to lose power. At first I checked the points, plugs and they were ok. It had its last Service in July 2007. So now I'm thinking that it could be a blocked Air Filter? It sounds just like a diesel Bus!! Any thoughts would be welcome. I have just found an Invoice of work carried out on the 22/01/07 stating that the car was lacking power and was "Runnung Lumpy" so they replaced the existiing on with "Coil Ignition?" for £131.41. Please can you help as I have to Long distances to drive next week for job interviews.