P0171 Ford -

Question

Poor fuel mileage, engine lays down when you stand on the gas,runs rough at start up

Answer 1

P0171 Fuel trim lean

When you set a lean condition this mean you are receiving more air to fuel ratio, one of the first inspection to look for is a broken MAF air duct tube, this definitely a lean running condition and poor fuel mileage

 Here a torn MAF air duct this cause a rough idle with poor acceleration , this will allow false air and a lean fuel trim condition