Hey all, newbie here.
My dad has a 1995 Subaru Impreza WRX (Japanese import, automatic estate model).

He recently bought on fleabay a device to supposedly derestrict it's top speed, it's a small component that fits behind the speedo and the cable goes into it, also converts it from KPH to MPH. Was a **** to fit (due to broken cable part but got it sorted so it now reads in MPH.

The car does seem, strangely enough less hesitant on kickdown and pulls hard (for a Subaru) thru the gears, but in top it stops revving at 4,500 RPM. It's not in "limp home mode" because it's not showing a check engine warning and it's not "on off on off" at 4,5k. But it just won't rev past it.

The guy who did the MOT did say that a lambda sensor needed changing which I have for the car (to be fitted) but would this stop the car revving in top? Is there some kind of magical electronic device stopping it doing so with a dodgy lambda sensor? It still won't go past 100MPH.

Any help greatly appreciated.