Slow cranking

Hi all,

im looking for advice, I recently bought a 2007 3.0tdi Q7 and one thing is really bugging me. When it’s cold the car cranks really slowly with the first turn of the key, far too slowly to start so I turn the ignition off and then on again and more often than not it will turn over much more quickly and fire up on the second try. I read the forums and saw that a lot of people have added an earth/ ground cable from the jump start post to the engine but I found that this was already installed to mine so I added a second one just to be certain that the engine had a good earth but it made no difference. What do I try next?

all help appreciated, thanks