406 High/Over Revving?

Hi, I have a 406 1.8i SX, since i have brought it, i have had problems with it over revving, it mostly sits at 1500 revs but the if i rev it to over 3000 it the revs itself between 2500 and 3000 for approx 30-50 secs then settles at 1500 again then 2 mins later it will settle at 850-900 revs i have been told to clean/change the idle control valve, of which a new one has fitted, but the problem is still there? I have done the ingnition on for 10 secs 3 times but this has not reset it? Is there anything else i can do?