Just to add to the thread after doing a coolant change I had a fault code saying bank 1 running rich.
I'm sure and was told this might have been a small air lock in the system.
After about a week of topping up small amounts all is ok now.
Also fault code has not come back.
As already mentioned, it might be the fuel system / pump, but use your OBD app to read the coolant temperature, the engine might be running a bit too hot (faulty thermostat)
Just had the same fault code on my car and also the revs at were dropping to 500 rpm when I took the foot of the gas.
Then it would settle to 750 after a few seconds.
All sorted now as the MAF needed cleaning with MAF cleaning spray.