I wouldnt say over time Graeme...It has only just raised it's ugly head after some 90K kms...but how. It prefers to drop the revs and stall out more often than not. It runs fine after a reset (at the key) ...makes me think it's something beyond carb/fueling issues, although a restart at the key initiates a fast idle setting until the ECU has sufficient temp sensor data to allow it to drop onto the ISC valve setting....
I take from your reply you suspect carby/fueling issues...Its good to know. I will assume this is typically the seat of the issues, as it did seem to get reported on the forum that was, quite regularly....
Ill do a sonic clean. If the injectors are crud packed, I cant see much future in washing it past valves and try burning it...I mean, where does it go, really ?
Has no one had to replace their ISC valve...? I remember pricing the valve for Otto many years ago who hoped it might be cheaper here in the U.K. but must admit, its my only recollection of the unit and its function...!
Seems strange it has developed overnight pretty much... 
BTW- Graeme, is a throttle body sync covered in the manual to your knowledge mate..?
TIA for any help !
TimR
Hi Tim, I would think the last likely suspect is the actual isc. As you say, on restart there is a different setup for a while and it confuses things.
You could be right about the injector(s) but I would first look at the balance of throttle bodies and the idle stop screw.
Vac gauges etc are not used for this. Thats a job after the physical balance is set.
The idle stop screw (the untouchable one) is hard to get at without tank off (or propped up ). Because they dont want you changing it without great care the end is just a square. If you do alter it you must take the bike for a run to be sure of result which is a pain since the tank is off (or propped up)
But I do know that that idle screw take very little change to make a difference and what you describe is exactly what it does when its a little too far out.
I made mine so I could adjust it a little from the outside. As to why it would change. Well that is interesting and I noted that the screw could "settle" a little just by the throttle closing(many times) and gradually "hammering" the end of adjusting screw. If the bike was set at the lower end of the range in the first place that might be enough to push it into the stalling area.
Throttle body balance is a tank off job and get access to the bodies so you can get a feeler gauge down there.
You can see the balance screw between the bodies and what you need to do is put a spacer (dont screw the idle stop) between the idle stop screw to open it a tiny bit then use a feeler gauge to get a neat slide between the butterfly and body. If the bodies are different adjust the balance screw to make them right. The oil tank side is the base of course and you are adjusting the other one to match it. Very small adjust or it might be perfect anyway.
Of course it could be a sensor or something as Nikk says but I think you must check these 2 first as they are the most likely.
If you dextrous with hands you can get to the idle stop screw with a pair of pointy nose pliers or similar and try a small adjust but I found it too easy to not know how much I had turned it. From stall to ok is maybe 1/2 to 3/4 turn of screw.
Since I did mine it has idled perfectly every time. I only had to do it because of fitting 43mm bodies and changing over the stratoliner cable cam etc which are different to MT.
I,m happy to be wrong but would like to know what you find-----------------