"Engine Systems Fault" Error Message

[rider007]

Firstly a little background about my car. It is a May 2005 LS Zetec manual with almost 20K on the clock which I have has for about 18 months. Up until about 8 months ago the car was running fine but since August there have been random problems engine problems occurring. Most common is when pulling up to a stop the revs will eratically raise or drop and possibly stall the engine. The engine has even shut down when driving a few times. Sometimes the engine will recover itself and accelleration away from lights will be normal other times there will be no power at all and it will limp away. It has been into my local dealer twice now to have ECU upgrades , battery terminal earths cleaned , injectors cleaned, throttle sensor cleaned and still the problem exists. Over the last month almost once every week I will get an "Engine Systems Faut" error message displayed for no apparent reason.

I run the car on BP premium unleaded most of the time. I can't detect any pinging noise so I'm not sure if that is the problem. Any suggestions ?, because this random inconvenience is begginning to take away the joy of owning this car.