The Hall Sender would probably not cause your van to run rich, it would just
make the van stop running if it was dead, or it would sputter (missing) at
the very mildest.
The temp II sender is probably your running rich culprit as it will cause
this.  You can test it with the Bentley manual to see if it is in spec before
you put out the money for a new one.  I have the Bosch ones for $40.  I don't
think VDO makes these.  The VDO ones are for the 2.1l Vanagons and are $9 but
won't work on your van (or syncro vans either, they take the earlier style
sender too).
Hope this clears this up for you.

Thanks,
Ken Wilford
http://www.vanagain.com
John 3:16

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