i have a mondeo st200 and when u put your foot down it holds back until u get to 4000 revs and then it lets go,i gather something is sticking but i dont no what

 

i was told that the 2nd butterflys stick on these not to sure tho

 

There is a device that controls the second set of valves and these give trouble with vac leaks etc.
As you probably know it works as a 12 valve engine until a certain point is reached then all 24 start working noit too sure on what goes wrong but think it is normaly easy cheap fix.
Although this is an ace site FMOC might have better answers if you have no joy here but still worth asking here first.
tabetha