I agree with David.  I have had this problem before, with the same symptoms
as Richard.

The ECU is adjusting the mixture by adding more fuel to the air/fuel mix,
since the O2 sensor is telling it is lean since there it senses no oxygen
left in the exhaust, over-enriching the mixture.

Runs horribly as soon as the engine warms up a bit, and the ECU feeback
control loop takes over.  Flooring it disables the O2 sensor feedback for a
bit.

Side effect is that you are pumping  too much gas into the engine, some of
which can end up in your crankcase, which will dilute your engine oil and
can cause catastrophic results with your oil pressure and bearings, and can
destroy your engine in fairly short order.

Change oil and filter immediately.  And maybe again, after not too long.

And this is unrelated to the Vanagon Syndrome, both symptoms and solution.

Craig in Cupertino

>
> At 05:05 PM 1/6/2016, Richard Golen wrote:
> >for a couple of minutes. Drove home and then disconnected the wires to
> >the O2 sensor. Took the van for a drive. Ran like a champ for about 5
> >minutes, and the loss of power, rich running, etc. started up again.
> >This is the first time its run this way with the O2 sensor
> >disconnected.
> >
> >
> >When it "idles" its runs roughly at 300 rpm and puffs out black smoke.
> >I've blown through 1/2 a tank in 80 miles.
>
> Find and clear the short to ground of the sensor wire.  It's probably
> where the shield ends on the bright green wire.  The insulation tends to
> crack there because of the sudden change in stiffness, and it get
> shorted by loose strands from the shield.
>
> You should have about 0.45 volts on that lead with ignition on and
> sensor cold or disconnected, measured with digital multimeter.
>
> Yrs,
> d