Could be the oxygen sensor, but I suspect the idle stabilizer.  I have these
for $24 each on my website (Dealer wants $185).  I have been surprized that
more 1.9l Vanagon owners haven't bought these as almost every 1.9l Vanagon
that I have ever worked on has had the loping idle which means the idle stab
is kaput.  I think most folks have tolerated it so long that they think it is
normal.  It ain't!

Thanks,
Ken Wilford
http://www.vanagain.com
John 3:16
Office (856)-765-1583
Shop (856)-327-0027
Fax   (856)-327-2242