If your 3i is the EFI version.TRY THIS:
Dissconnect the black earth cable from the battery.(remembering radio codes first).Leave it for about 45mins.Then reconnect the battery and go for a drive.Your (ECU)engine control unit has forgotten what to do, so you have to tell it.The ECU is self learning.For the first 5 miles it will record how you drive.If you drive nice and gentle it will store the information and that will be how it performs from then on.
If you drive it like you stole it then it will record how you are driving and expect to be driven like that all the time.
My 89 xr3i is faster in every way compared to my mates mk4 RS Turbo.
The idle is not smooth,But the performance is great and it doesn't drink anymore fuel than normal.
Paul