I when for a test ,
Whit the vac. disconnected the butterfly is open( relax mode) and the car dose the same, then I apply vacuum whit a T and butterfly closed, I deaden notice a change in the engine sound or rmp , the car improve a little but the jerkin is still there .
Regarding that butterfly suppose to stay close during normal drive ?
The EGR valve can produce this symptoms ?

@Stevo
I added the car to my vehicles and deaden appear as my signature , where is that section ??
Thx