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My name is ***** ***** your Coleman furnace a Manufactured home type or the upflow basement type?
Ok could be a poor ground for the furnace, however depending on your area it could be a spider web or silk worm nest in the main gas orifice, this will sometimes let enough gas trough the web to ignite but not enough for the flame to develop fully and make good solid contact between the flame rod and the burner head itself. Do you know how to check the burner orifice?
Tell me when the last time the furnace worked normally.
there should be three wires coming in the side of the furnace one black one white nd one bare copper the copper wire should be wire connected to the furnace cabinet some how could go to a green ground screw could go to a green wire screwed to the cabinet be sure its connected tight.
The Main burner orifice is connected to the gas manifold valve, shut the gas off, remove the 2 5/16" head screws from the valve bracket and slide the orifice tube out of the furnace burner you may have remove this when you changed the flame sensor. the orifice is the brass nut on the end of the pipe, look down into it with a flashlight be sure its clear if you see a web remove it with a tooth pick or pipe cleaner sometimes you have to remove the orifice from the tube it is 1/2" a box end wrench works best
Another thought that comes to mind is that the male female connector that is above the flame sensor may be broken not making contact.
If you have a multi meter that reads micro amps DC when can test the flame circuit to be sure the board is sending out the 3.5-4 ua signal to sense the flame. There is the possibility that the board is bad but you should examine it carefully for corrosion or burn spots. because it is and expensive part no need to change it without a good test.