Help please!!
 

Help! My car has gone weird all of sudden. It was fine then I noticed the speedo wasn't working. But then I noticed it won't rev over 4000 rpm it starts coughing and spitting. Also the side lights are but the switch is off!! Is this is a fuse problem or a bad earth connection???

Speedo not working causes limp home mode (limited revs and boost as you've found out).
Is the switch on top of the steering column on?

Thanks for your reply. Yes I realised shortly after posting that I had the parking light switch on! Doh. Limp home mode makes sense. I know that I've got a converter attached between the gearbox and speedo if that's gone or the gearbox sensor are they costly parts? Thanks.