USe the hidden menu to read the engine temp, see if it IS warming up properly or always running cold, if it IS running cold then see how many thermostats you have ( maybe 2 ) and replace them.

Plus there's a section on here where folk have registered what their real mpg on different models are getting, see if anyone else has put in details for a 2.2 petrol auto.

 

If you are driving very short journeys only that economy might be as good as it get for the auto. I was getting 18mpg in my manual doing 1 mile journeys to work and back.

If you are doing longer journeys then that is poor mpg.

It is well worth getting a fault code reader and checking the engine ECU has not got any fault codes stored in it.

The fuel filter is worth changing if it is a few years old, this will probably not help with the poor economy though. You could also check all the wheels spin freely, in case a brake caliper has seized up.

Another thing worth checking on the diagnostic is the fuel trims - the long term fuel trim (LTFT) should be close to 0, or ideally within +/-2%. Air leaks on the pipework and in many other places are common on the M54 engine, and these cause the LTFT to go very high, which can effect fuel economy.