hopefully someone can help me here as this is really doing my head in now

basically my Si will hang at around 1500rpm and seems to take ages to drop to a normal idle speed. when i first start the car it is fine but it is only once i move off, for example when i drive off and come to standstill it stays at a high rev but will drop eventually. it doesnt seem to matter if the car is cold or warmed up nicely either

i have cleaned the ISCV, changed the TPS, cleaned the MAF, had inlet checked for airleaks, throttle body cleaned and recently changed the speed sensor but it still does it

anyone got any ideas??

John