What sort have thing ave been looked at to try and solve the problem?
The ECU on the mini's are called the DME different name same thing :-). The DME is self adapting meaning it learns as you drive, ie you driving style and engine profomance. If you do engine modifications to your car its advisable that you reset the DME. That might be why you had no luck with you k&n filter.
It takes a little while to learn.
A remap is basically rewriting or tweaking the software perameters in your DME this takes it out side of what the origanal DMC operates at there s no real need for this until you start to change some major things like cams, bigger injectors and very modified head
A service is always a good place to start, if you are going to fit a pulley you will need to change the plugs to a better spec you need to go up a heat range most guys change to iridium BKR7EIX these can be obtained from spark plug .co..
Always check the plugs are tight to they loosen off and strip the spark plug hole I fit mine and then check them a week or so after.
I would advise you to to fit a tensioner stop to protect your engine if the belt breaks.
When you change the pulley are you changing the intercooler as you will need to there are a few options,
You can change the fuel filter I will find a link for you it's always worth doing it never seems to get done http://www.mini2.com/forum/first-gen...l-problem.html