Can anyone help me with a 4 month old Cairn pup who is terrified of cars driving past at speed. Reacts by leaping at the car with a blood curdling growl and would chase the car if allowed to. He's ok if the car is driving past slowly.
Also eats his own faeces all the time as well as any other he can get his paws on.

The problem with cars is always when he is on a lead. I never walk him off the lead near a road.
A

If he is okay when a car drives past slowly then I would not take him along the fast roads but put him in the car and drive to the park.  Meanwhile you could take him to Sainsbury's car park and find at what level (speed and distance) that he can cope and build up from there.  Everytime he is frightened by a car and reacts how you described then his fear will be reinforced and his coping strategy will become a learned behaviour. 
Sally

Hi Sally, I live in the country so we are able to walk to fields that surround our village and he'll see one car every 10 or so minutes. He can cope in Sainsburys car park as  cars tend to drive slowly. I have taken him to our local town and he was constantly leaping (on a lead) towards the cars.
I've taken your comments on board and will walk to our closest fields for a while and maybe a few more visits to Sainsburys and get my husband to do drive pasts at varying speeds. It's interesting what you say about his coping strategy becoming a learned behaviour. Thanks for your help.
A

If the dog is coprophagic it may be connected with what you feed; if you have no desire to change his diet then the addition of digestive enzymes, either in tablet form or via papaya or pineapple may improve this; generally dogs consume faeces, both their own and that of other animals, because there is some food value remaining in the stools as the food is incompletely digested.

Generally speaking because commercial dog food has a high grain content.

HTH