Hyundai Repair: poor gas mileage and black smoke, coolant temperature sensor, air flow sensor

Question
I have a 1995 Hyundai Accent.  The exhaust puts out black smoke, especially durning accelleration sitting still and driving.  Gas mileage it bad and it sometimes has low power.  When I remove the plugs they have black smut all over them.  What could be problem?

Answer
This sounds like the fuel is not fully burning, usually caused by too much fuel.

Check for the following:
1.  Exhaust leak.
2.  Faulty oxygen sensor.
3.  Faulty air flow sensor.
4.  Coolant temperature sensor reading too low a temperature.
5.  Bad gas.

I'll say that I've only seen the bad gas instance one time.  But the car did run very poorly, and the plugs had the soot on them that you describe.