bear in mind im not in the states and wouldnt know a volvo egr valve if i fell overone....but...

i have imported a japanese deisel into the uk which comes with an egr valve (legal requirement ion japan not in the uk.

The same engien was used in the uk without the valve, the valve always ends up stuck open through gunking up...common oslution is to place a blanking plate between it an the manifold - other common solution is to just take it off, install two blanking plates and plug the vacume line that controls it...

currently im on the blankin plate method while i vavlidate it HAD stuck, to be followed by the two blanking plate method while i strip it and (attempt) to clean it...of i an i will chuck it back on to do my bit, ifi ts junked it will be left off...as they are really expensive!

anyway..jsut a thought if the issue is rotten cars up north but ok motors cant you just remove all the californian gubbins? and replace any bits with stuff salvaged from ones with rotted out bodies?