know what you mean m8 (hard to explain) it could be one of your switches on the engine or it could be your air/fuel mixture there is a mixture screw on the pasanger side of the bulk head but you wont know what your emissions are so best bet is to get it set up on a rolling road might cost you 100 quid or so but its worth it,other wise it could get expensive replacing bits you dont need
hpoe this helps m8 good luck