Ive got a 56-plate Vectra 2.8 T, on the inlet manifold at the back in the middle theres 2 pipes going in, under that theres a vacume solenoid with wiring plug going to it what does this do or control, mine is clicking on and off like a light switch.

Car is poorly and need to know what this part does/controls to eliminate if thats the fault or i need to be looking for something else.

Thanks for your help guys, my 2 local dealers are of no help/use.