There are a lot of members there and you would probably get a lot of responses.
Some Icelandic Horses are similar to yours just by birth. Some are born calm and some are nervous.
If it was my horse, I would start by checking his feed. Nothing hot, no alfalfa, no supplements without knowing what's in them.
I would give a low sugar grass (I use bermuda for my horses), and supplement with something like TracGuard, or B vitamins, or magnesium. These are all supposed to be calming things.
Then I would start working with him with clicker training. Touch the target, click, treat. It usually helps with these types of Icelandics.
