Hi all ive got a combo cdti and it is overboosing, so much so it blows holes in the boost pipes,

Ive done some searching and i think i may have found the problem but need a little more info.

Ive checked the wastegate arm and its free and connected. Ive also followed the vac pipes all the way to what i beleive is the boost solenoid valve which if i move the rod underneath by hand operates fine but it doesent when the engine is running.

There is a vacuum at the pipe also.

Question is, how does the boost solenoid work? is the rod underneath just connected to a spring?? should the vacuum increase and operate the rod? or does the boost pressure sensor operate a motor which operates the rod?

Ive had to unplug the vac hose to drive the van as the turbo is running full boost even at tickover!

Please help! Mike