2007 Navigator 80k miles. Just got new coolant flush coil plugs and spark plugs. It has full power when getting on it but rough at idle and stinks of gas very bad. I took it back after tune up and they cleaned maf and said change oil. Well I had 700 miles on last change but did anyways. Still bad. I was told to bring it in have plugs removed blow carbon out of cylinders and retorque plugs. Does this sound like the issue? I believe this could be the issue if this is as common as he said it was but still skepticle. Should they check anything else? No see codes...