Although I have replaced all 6 glow plugs on my 2005 Allroad (yes all 6 were open circuit!) cold starting is still not as it should be. (Please see my post 2 weeks ago where I have described the job done) When the ambient is 4c or more then the engine will start first time but when it is any colder it really struggles to get going. Whilst I had the plugs out I checked the supply to them with a test lamp which was staying on for about 10 seconds so I am sure the problem is not with the relay etc: I have tried the old trick of switching on the ignition twice to allow the glow plugs to get hotter, but still I have to keep the starter going for a prolonged period whilst the engine begins to fire, seemingly on one or two cylinders. When it eventually picks up then it runs perfectly. In fact the engine is absolutely spot on except for this issue. Other diesel engines I have owned (Mercedes and Jeep) have always started very easily no matter how cold, so is this something unique to the Audi 2.5tdi ?