My father just got our '84 GL through NJ emissions.  It failed the first time
(for hydrocarbons) but it was time for an oil change anyway so he changed the
oil, added a 1/2 quart of Marvel Mystery Oil (to help quiet the lifters),
added some injector cleaner and two tanks of premium fuel.  Took the van back
a week later and passed with no problem.  Note: Van had a recent tune-up with
new oxygen sensor, cap, rotor, and spark plugs (autolite platinums) a few
months before getting inspected so I knew that these weren't at fault.  Also
I had timed the van myself with a timing light so I knew the timing was good
and I had also replaced all vacuum lines at a prior time.  When you keep the
van in tune and know your van, it just makes your possible causes of failure
list shorter.
Ken Wilford
Van-Again
John 3:16
PS This van idles smooth like my '91 Carat (unlike most Vanagons that I run
into however which have a loping idle.  No it is not supposed to idle that
way!)