ok 2000 s40, behind the driver rear tire theres what looks to be a fuel pump assembly of some sorts. is this the main pump or a pre-pump simialr to the older 240 series? i can not seem to find any information on this part. my problems with vehicle seem to point to a faulty fuel pump, or a fouled timing belt. im leading to the pump assembly as its a very noisy thing, can actually here it pumping or clicking.

 

That pump is for the fuel evaperative system.

 

ok thank you tech , also would this thing possibly be a cause of a rough idle and "stumbling under load" symptom ? seems the noise i here comes from this apparatus. at present im cleaining IAC and replacing the little hose from IAC to intercooler, after reading the awesome writeup at s40concepts.net, seems its a very cheap place to start, and hell who knows i might just get lucky and dodge a fuelpump bullet

 

NO that will not cause that.
That pump only works at certain times when the car is running.
Bascially it puts the fuel tank system under pressure to make sure there is no leaks.