that does make sense actually... ir has had the head skimmed when i redid the head gasket, it has only 1 skim left in it the machine shop guy said before its no use for turbo engine. even though i used the thicker cometic head gasket to try to overcome the upped C/R do to the skim, it still may be enough to cause it to pul less vac, just out of interest what should a good engine pull at idle with no vta dump valve? mine pull down to -0.7 bar and stays steady there at idle.