Done a search but not come up with anything on here.  Think I have narrowed down where the problem is coming from by chance due to the hot weather.  Switched the AC on late last week and the idle smoothed out. Its not bad but frustrating when you know how smooth the engine can be when its not happening.   From what I can see online the options seem to be drive belt tensioner or more likely the alternator clutch pulley starting to play up.  It does sometimes make a strange noise on star