Hi, first post and absolutely no clue about cars ....have bought a 1.5dci 2008 megane and when on motorway in fourth or fifth above 50mph I have check injection and spanner light on....never happens in urban driving. Car starts first time and no apparent loss of power. Had rac out who said fault comes up as df025 preheating diagnostic connection. In my very limited knowledge this is glow plugs but car starts almost instantly and check injection message never comes on until on motorway over 50 mph. He said it was not an injector as fuel pressure was as expected and car is not missing. I'm feeling vibrations in fourth and fifth gear until I get to 2000 revs tho...goes away then...unsure if this is unrelated problem? Any help gratefully received.