Thanks for your feedback Phil, always helpful.
My only question is, surely we would have the same problems when the car is cold for this to be the problem?
Well as far as I see it, we have different filters but the same problem. Cold strt is fine, revs blip, drop and then level off. When warm, revs blip, drop, but dont recover. I get the feeling that the airflow drops too much as the valve closes and it cant twist it open quick enough to recover. The fact that sometimes mine does recover suggests that somethings sticking. Either that or the warm idle needs uping a bit to cope.