Here is a short description about the affect of  the trotty tolt on the Icelandic Horse.
You aren't free from the tolt yet!
Tölt V  
 Cleaning Trotty Tölt 
By Arnthrudur Heimisd
A horse can be trotty in the tolt.  The footfall has been explained before, but looking at the trotty-tolting horse, you see something that might be described as an abnormally short distance (compared to clean tolt) between the front leg and the hind leg on the same side.  When
riding the trot-tolt, the up-down motion is more than in a clean tolt or pacy tolt, so it is more uncomfortable to ride.  If you are training a horse that is a definite trotter (doesn't ever tolt or pace a single step in pasture), and haven't done it before, it might even be difficult for you to find the difference between the trot and the trot-tolt.  To find the difference, allow the horse to trot, and really concentrate on how that feels, before you change your seat.  That way you can feel the
subtle difference, so that you don't correct the horse  when it is really doing the best it can.  If still in doubt, get someone to watch you and tell you if the horse is trotting or doing something else.
Horses that do trotty-tolt can be doing that for many reasons, not necessarily because of lack of talents.  Very often you can't say very much about the natural gaits and capabilities of your horse until after starting and then more training.
It is more difficult to correct a trot-tolting horse if it has a long back, a stiff (straight) back, a neck that is low on the withers, or a very tall croup.
You have to help the trot-tolter to free its withers, be sure that the saddle isn't lying on the withers, even move it a bit behind the point where it usually lies on the horses back.  Keep in mind though, to be moderate, as the saddle can sore the back of the horse if it is to much backwards.  Never use weights of any kind on the front feet of the trotty tolter, even remove the front shoes if nothing else works.
The principles behind riding the trotty tolter are, maybe surprisingly, very similar to riding the pacy tolter, except that the trotty tolter is often very simply lazy.  Teach the horse collection (so it uses it's croup and doesn't hollow it's back) without pressing the head to vertical in the tolt.  The head may be in the vertical in walk.  Ride slightly downhill, to free the withers of the horse and get it to use it's behind more.  Sit a bit behind the place where you usually sit in the saddle, but keep a good seat.
It is very difficult for a trot-tolter to tolt on an uneven, soft road.  Also, as he can only tolt very slow to begin with, it is best to tolt-train this horse alone, as other horses riding with it disturb it's
concentration (as they either go too fast or too slow) so it just trots.
Do anything you can figure out to encourage the lazy trotter to love a bit of speed.  Use a crop (moderately), voice signals (sing operas if necessary), do an occasional brisk canter, train the tolt when the horse sees the barn, ride different trails if you have the opportunity etc.  Very often you can only do tolt-training on the way home, because the horse is lazy.  This same horse might trot briskly, but hasn't got enough go to tolt without this extra effort from the trainer.
If the horse is a trotter and nothing else, start training the walk as it was tolt, using all the same clues and collection.  Increase the speed once in a while, so the horse walks fast in a tolt-posture.  Train
this horse often, maybe riding it for 20-30 minutes 5 times per week.  Ride the horse in increasingly fast walk, until one day you're riding slow tolt.  Always train the tolt for short distances, maybe 50-200 yards at a time, giving the horse an opportunity to stretch the neck in long reins for a few steps after the tolt.  Do this many times in the ride, doing other gaits in between.
Softening exercises, like sidestepping, stopping, transitions, backing etc. help to free the withers and help the horse to give in in the poll.  Remember that you want the horse to give in in the poll,
without leaning on the reins.  Do small half-inch movements to stop the horse from leaning, and becoming more on the bit.
If a horse only trots, start doing this while it is still young.  It is increasingly difficult to train a trotting horse to tolt as it becomes older.


                                            Happy trails.