please help,i've bought a fiesta turbo ofab with t3 ect,when i got it the idle was 1500rpm,now when revved it seems to stay up to what you rev it to and hold for around 3 secs before dropping down to 15-2000 rpm,iscv was changed today but is still the same as the old stripped and cleaned one,if i unplug the iscv and rev it the revs drop instantly rather than holding,the car drives and boosts fine and will idle by tensioning the cable fine.

where do i go from here?

Lee