I know it's not a WBX motor but it is Bosch and uses many of the same
parts as a Vanagon stocker.  Plus I know there are list members with other
similar VW motors and knowledge of the Digifant EFI system.  Here goes:

  This particular motor is still  running super. No issues other than this
recent minor irritating new behavior.  Gas mileage has not changed in about
30k miles I have put on.  It's an 8-valve 1.8liter VW motor from a '92
Jetta/Cabriolet/Rabbit stuck into my 5sp vanagon using diesel van
peices/parts.  It has no cat and a straight through Magnaflow SS muffler.
  I've recently noticed  that more often than before it sometimes 'pops'  a
bit, softly..on deceleration..As in:  when downshifting and coming to a
stop.  It has always been a little prone to this behavior , but until
recently, only when it is in 'warm up' mode..like before the idle circuit
had stopped and the idle slowed to normal..But recently it has begun to do
some very mild popping as I decelerate even when fully warmed up.....not
every time but it occurs more often if i have just done a hard acceleration,
then let off..Like in stop and go traffic. If I floor it, then drop the
throttle and coast down, it goes..bapp bap bappity put put..did-dow dow
dow....not loud but like that... It seems like there may be some kind of
throttle switch that might be 'going south' or something..allowing some
unburned fuel to pass through the motor and then maybe ignite in the muffler
or on its way out the exhaust system?..Or perhaps I have an injector that is
working at times when it shouldn't be or leaking fuel into the fuel rail
using the vacume created by deceleration?...but that would give me a loss in
fuel mileage, right?
  This behavior is not really bothersome other than I've noticed it now so I
want to figure it out and put it back exactly to rights.  I sometimes lately
see pedestrians lately turning as I go past, smiling at the old Hippy in the
'poopy-colored poopy-sounding'  Bus..  I don't like to draw attention like
that.  Some official might notice and  be inspired to" help ' me and the
enviornment by legislating  my 'clunker' away  and giving me the
option to charge a  brand new PT Cruiser or an Element or something...
  Any hints or ideas where I should look?
  Don Hanson