Adam -
  My '85 did the same thing. Intermittent failures / faults will drive you nuts! But my solution ended up being the good ole O2 sensor. I later had a slightly different rough running / poor milage problem that I tried EVERYTHING to fix - new distributor, cap, wires, rotor, plugs, brain, temp sensor II, and could not get it to go away. It turned out to be the ignition module. After I replaced that, my idle was steady and smooth, and my milage is now on the high side of 17 MPG. I did not consider the the module as the failure point, because I thought that the module was one of those "works / stops working" failure items. It was not. The '87 does not have the same igition set-up as the '85, but there are components that do the same jobs...

Adam Thacker <87westy@THACKER.CA> wrote:
1987 Vanagon GL
I am having the exact same problem as the person below but when I tried his
email address it bounced on me if anyone has any Ideas of why this is
happening to me or who Knows Neal Helfman's New Email address I would
appreciate a reply. Like I say I am having the exact same problem as him I
just have not replaced all the parts he did.

Original post here.
http://gerry.vanagon.com/cgi-bin/wa.exe?A2=ind9607&L=vanagon&P=R28890&m=2570
7

Subject: Help:87 syncro running bad

I am the consequential owner of a 1987 Vanogon Syncro. I need help with an
electrical/ignition problem that won't go away for more than three months at
a time. My van acts like there is water in the fuel and runs very rich and
coughs black smoke. Power loss is evident and the idle is very rough.
Every
once in a while it runs wonderfully as if a mechanic were standing right
there. Other times the power loss episodes are erratic and random. When it
is acting up pressing the accellerator to the floor clears it up with a jolt
of power and accelleration... let up on the gas and it starts jerking and
coughing again. It has new heads; alternator; waterpump; CPU; plugs; wires;
cap/rotor; air filter; etc.... Help me!!!!
My name is Neal Helfman and my e-mail address is;
NHelfman@aol.com
If you know of anyone who specializes in Vanogon electronic fuel injection
please give them my name!!!! I have $$$$$ to spend for the correct
diagnosis!!! Thankyou r

Thank you
Adam Thacker
1987 Vanagon GL