Hi all, new to this forum although I've lurked through many posts, I'm wondering if anyone could shed some light for me about my car.

It's a low mileage ford mondeo 2.0 petrol duratec on a 05 reg, I've been going round in circles trying to solve its p0171 dtc,

So far I've replaced,

Coil pack genuine ford
Spark plugs
Ht leads
egr
Air filter
cam sensor
fuel pump (pattern) to rule out low fuel pressure
petrol filter
Pcv hose
Swirl flap delete and bank 1 sensor 1
map sensor

And I've had the injectors, cleaned and tested and all are functioning correctly,

I haven't touched the
Crank sensor
Thermostat (believed to be good, car on 60k)

Symptoms are popping/ backfiring in intake can be heard, some times a lower case r comes on the little information screen on the left screen, under the tach and cooling fan runs at 96 d.celcuis

Any help is appreciated, regards bobbin.