Engine malfunction nightmare issue FOCUS

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Any help would be gratefully received.  I have a 08 Ford Focus  1.6 diesel. A few months ago my car showed an egr fault but I didn't replace it at the time. I ran the car nearly out of diesel (20 miles left) after a few days the engine malfunction bleeped up and I went to the garage and they said egr valve was showing as the fault so I replaced it. When the new egr valve was fitted it still came up as egr valve fault !!! So they blanked it off and still the same old crap engine malfunction and going into limp mode  but again showing no more fault than the egr valve again.  Some times the engine malfunction doesn't shows up on starting and you can drive for a while then comes on whilst driving. I was kinda noticing it around 2000 to 3000 revs. Any help please guys on possibly what's wrong ?  ( why do ford have the worse engine malfunction bleeps )