GM-GMC: 89 GMC Stall, coolant temp, black hope

Question
Hello,Have an 89 GMC, 1/2 ton, 5.7 litre with 84000 miles. Have not had any problem at all until my wife went to start it and it did not. It started after several tries for me, check engine light came on drove it 65 miles no problem. Next day it started but runs rough.I did check codes it was code12 coolant sensor. My manual says this may not fix problem.Can this sensor cause engine to run rough? Have you seen this type of problem before? Thanks for help.

Answer
Not uncommon.  Replace the sensor, located at the front left of the upper intake if looking at the engine, beside the thermostat.  Sensors are cheap and when they go bad usually default to a cold coolant temp, which means the pcm will dump lots and lots of fuel to the engine and make it run rough and likely smoke black.
Hope this helps