buy some 'carb cleaner' from halfords.
Take off your airbox/filter exposing the throttle body, give it a wipe down, the get someone to start the engine and pulse the accelerator up to 5-6k revs and down again, over and over. You'll notice the butterfly opens. Spray approx half the can of carb cleaner constantly into the TB.
When finished leave the car running, and take it for a good run. Let the VVT kick in (tip from Mr. P).
Here's a dirty and a clean Throttle Body



