John, I know it sounds basic but have you checked the oil level? You've just done a long drive (LOS) and I think it is worth checking all the obvious things.
If everything is normal, and the engine is behaving (ie no rough idle, down on power, in limp-home-mode), I'd try resetting the ECU. You do not need to disconnect the battery, you can use the switch under the bonnet that powers the entire car down (like a master circuit breaker). When I've let the battery die, my car will throw up faults and this is the way to clear them. The process is: pop the hood, hit the reset, leave the car for 5-minutes, push the switch back in, start the car and take it for a short drive. This resets the ECU and clears the error messages. If you have water ingress or genuine issues with the engine, this won't clear them; however, it can help if you have having 'ghosts in the machine'
