Thanks for the replies, First of all i,m in Newcastle NSW .The only thing thats been changed is the mufflers their sceaming eagle i was told that they would not cause any hassle as far as the ECM goes . The bike has been riched up had leeds replaced of which one had broken down,fuel system flushed fuel sensor replaced,thats whats been done so far the next thing is there replacing the engine mounts after that screaming eagle tuning kit will be fitted to get more adjustment after that they,ll go for the computer. This is all good but it is taking a long time to get parts and it,s a lot of riding time i am missing. A quick run down on the sporty in short the bike performs great in all other aspects accept when trying to cruise and you get this back and forth horse bucking also after about 20 minutes of riding you pull up at the lights and it will high rev for about 10 to 15 seconds.Thats where i am at the moment i have to ring harley today to see whats happening i'll let you know how i get on . Once again thanks for the replies BUFUS.

Sounds like the ECM to me.

Check your fuse box i was having a similar problem with high idle the fuse box was corroded i cleaned it up with some cleaner from the auto parts store in town n smeared it with dielectric grease. haven't had any worries since was all so getting a bit of surging with stock ecm i have fittied an after market computer n bike has been running a lot better.

Mate PM toxic, he had an issue with high revs on his sporty and it was a very simple fix...just a thought.