have you had the car plugged into some diagnostic equipment? maybe this may reveal the cause?

Sorry to hear of you problems..few things for you to try here and firstly from what I have read about the Idea on the internet and forums over the years they have lots of EGR problems on the 1.3 multijet and the same problems are now appearing on the multijet pandas..many owners blank off the EGR for smoother running on the idea and its a constant poblem on many other diesel cars as well..also try giving the connections to the computer a clean up with contact cleaner..MAF seems to play up quite a lot on these cars as well so try unplugging that to see if there is any improvement..as Scottie has said it might be worth you getting the car pluged in at your local garage to se if there are any codes logged onto the ECU..