hello i'mnew to merc.i just bought a 1982 300d ,and it needs a lot of help .the vac. pressure is at 10hg, and the needle bounces around like crazy at idle.just ran some deisal purge through and changed the filters, are they suposed to be blk. motor still runs rough andhas no power at idlecan this be because of air in the fuel system ?the primer pump leaks like crazy when you try to primethe filter.