'87 4kq fuel system problems

["Aaron Peloquin" <Aaron@Peloquin.com>]

Symptoms:  black smoke coming out of the tail pipe; excessive fuel
consumption (below 10 mpg); running extremely rough because spark plugs
caked with carbon desposits, in some cases clogging the gaps; very black
oil.

Took it to Bellevue Motorsports, they replaced the air hose that runs
between the ISV and air intake plenum and the O2 sensor, and they reset the
fuel-air mixture.  I replaced the plugs and the air filter.  The cap and
rotor are new and the wires < 1 year old.

Ran better than ever for a couple of days.  I noticed that fuel consumption
still seems high (hard to guage with no working odometer) and now under
acceleration the smoke is back.  Also starting to feel a minor hesitation.
Pulled one of the plugs and it's already black from carbon deposits.

Any ideas on what is happening to my poor car?

TIA,
Aaron Peloquin
Kirkland, WA