Use to set about 200 miles or so now less than 50. Idle sounds like a deisel rattling valves. Sets very fast if put under load. Found dry roted hose to brake booster replaced no codes 2 weeks later setting less than 50 miles. Cant find any vacuum leaks. Poor milage. Under load every now and then about 6 monthes it will set P0171.
171,174 codes are from vacuum leaks, low fuel pressure, mass air flow bad or pcv valve. I suggest a shop with a smoke tester to smoke the intake system for leaks. I would start there before exploring other possibilities.