I kids picked up a 1993 Jimmy with the 4.3 (not sure on the vin code) and it runs rough and puts black soot on the ground on start up.. It seems to run better once the engine warms up and the Service engine soon light comes on.. I checked the codes and it has a 44 code (lean mixture) After reading on here, others mention checking the Temp Sender, well there temperature gauge doesn't work..

Is it possible the faulty temp gauge is causing this problem ???

Usually the coolant temp sensor (not the gage sender) would cause the engine to be rich when warmed or lean when cold, a scan will allow you to see the temp inputs to the pcm.