HELP PLEASE??

I have a a corsa as described above and the Engine management light keeps coming on. The car goes into "limp home" mode and doesn't accelarate properly at all. I took it to vauxhall in the first instance who, surprise surprise, diagnosed the problem to be the Engine Control Unit (ECU) after replacing the coil pack and sparks plugs also. I had the ECU replaced and this did not rectify the problem. I then had it re-diagnosed by a different garage as the head gasket which, as the car was blowing white smoke, was understandable. The car no longer blows white smoke but still does not drive correctly and the engine managament light still comes on. I can't take it on the motorway as it just automatically goes into limp home mode. I have since had various other parts replaced and checked :- Engine Loom, Inlet manifold, injectors, crank sensor, fuel filter, fuel pump, fuel tank, airflow meter, throttle body and the throttle pedal. The car is running and running better obviously thanks to all the lovely new parts it has on it but, it is still doing the original problem, just on a less severe scale!?!?

Please Help?? this has cost me well over a grand now and I can't afford to plough much more into the car :(

What do we suggest guys??