Same story on my '87 Westy.  Been like that since I installed the new oxy
sensor, generic Bosch, from The Bus Depot.  Unplug the black single lead and
the engine has no hesitation but does seem to consume more gas.  Plug in the
black wire and the hesitation comes back.  I also have the idle surging
problem and have not tracked the cause of that yet either.  So I have no
solution to offer up here, just confirmation of the same symptoms.  I have
not had time yet to do a full check of the throttle body switch, the idle
stbilizer valve, the idle stablizer control, air flow meter & harness or the
oxy sensor to see if any of thse items are out of spec and the cause of the
hesitation problem and surging idle problem.  I may get on it this week and
try to figure it out. I'll report back my findings when I get them.  All
these electronic gadget just bug me, and I know a bit about looking into them
!  I can just imagine what someone who doesn't have a clue about all this
electronic stuff has to go through to get these problems solved.  Good luck !

Cheers

Frank Condelli
'87 Westy & Lionel Trains
Almonte, On
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