I can understand you there China !
If I was you though ( and because I'm skint ) I'd do a full fault check first before buying anything..
Things I'd check ( apoligies if you've already done this ) :
DV valve - remove the valve and suck the top small pipe - you should hear and feel the valve move, when you stop sucking the valve should spring back into place.... Suck/blow the other 2 ends - there should be NO movement or leakage of air.... if all checks are fine, you're DV isn't at fault ( no need to replace )
Hoses - the 3 hoses attaching to the DV, are there any cracks/splits, if so replace if needed... also are the hoses very old, very soft ? if so when you boot the car then the hoses will be getting sucked in ( loss of power )
Spark Plugs - am I right in saying you've changed the plugs ? if so did you torque them down correctly ? worth double checking.
Air filter - is there any sh!t in there ? check and clean if needed... Do you have an induction kit ? if so your car might run like sh!t in town but fine out of town..
Fuel - Do you use cheap crappy watered down petrol ( tesco's bad for this ) if so then you need to get rid of any excess water from your fuel system.... Google water in petrol for a very cheap fix... simply changing petrol supplier isn't good enough, you'll need an alchohol ( type stuff ) mixed to your petrol ( only once ).
Nearly forgot... Throttle Body clean is worth doing to...
Good luck China !! and let us know how you get on..
