Classic symptoms of a problem with the OX sensor wiring or the sensor
itself.
The ECU just IGNORES the OX sensor signal until the coolant temp sensor
tells it the engine is warmed up.
THEN it uses the OX sensor signal to adjust the fuel mixture for best
ratio. If the signal it sees is screwy it will badly mess up the mixture
trying to correct it. It won't do this until the engine has been running
for a few minutes.

Many times this problem is caused by someone splicing a generic OX
sensor into the OEM wiring.
The splice becomes a problem either right away or some time down the
road.

Another common cause of OX signal errors is the GROUND for the OX
signal. This is the small brown wire that comes out from the same small
bundle as the hall connector to the distributor. The brown wire has a
small ring connector on it and it gets attaches in various places as
different people work on the engine. It should be removed and cleaned to
shiny metal. Then it should be screwed down to the engine at a place
where it is against shiny METAL. Commonly it gets screwed down against
the plastic of the oil breather tower and this is not a good place.

Mark

Andy Morse wrote:
>
> I'm beat ... the Vanagon gremlins have won, I'm tired of wasting my
> time...whining over. I'm getting the Syncro towed next week to the mechanic ugh! At
> cold start it's absolutely fine and once it warms up about 5 minutes of idling it
> starts to sputter, no power, back fires and once in a while regains power for
> 10 sec or so. Totally undriveable still. I've cleaned all grounds installed a
> new cap, rotor, plugs, wires, temp sensor and I installed the capacitor for
> the air flow as well. What the F*** is wrong with this van! Anymore
> suggestions...
>
> I miss the simplicity of my 71 Westy
>