Question

Ford Mustang 4.0 V6 P0191 comes after the vehicle has been idling for more than 5 minutes, also seems to happen when the outside temperatures are above 85 degrees...WHY? current mileage 66k

Answer 1

P0191 Fuel rail pressure Sensor "A" circuit range / perfromance

Fuel pressure has to be tested, when you have a P0191 set the fuel rail pressure has detected either a low fuel pressure to the sensor  or high fuel pressure,