For whatever its worth check your coolant level. The black plugs spell out "rich running". Read the link I send you concerning coolant sensors.
Coolant Sensor
The water temperature sensor communicates information to and from the computer. If this has failed to work properly, it would definitely create issues like the one you described. Before we condemn the sensor let’s make sure the coolant level is correct and the antifreeze is properly mixed. The antifreeze should be 50-50 one part antifreeze and the other part water. If the mixture is wrong, it could affect the sensor. Most people do not pay enough attention to this little device, which can give you many problems. Learn more about Coolant Sensors, Click on the link provided below…
http://www.mightyautoparts.com/pdf/articles/tt67.pdf
Another thought...
Chevron Professional 3-Step Fuel System Cleaner
Chevron Professional 3-Step Fuel System Cleaner provides three critical engine cleaning formulas in an a three-step application.
§ Step 1 – TECHRON Concentrate helps clean deposits from fuel injectors, carburetors, ports, valves and combustion chamber. It also reduces knock, ping, and run-on and helps lower emissions.
§ Step 2 – Induction Cleaner helps remove harmful carbon, varnish and gum deposits
§ Step 3 – Throttle Body/Air Intake Cleaner cleans throttle body and air intake systems
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