A while ago i put a post up (I think) about my Engine management light coming on when i put my foot down in my 2.0l petrol....
I finally fixed it, by accident

Symptoms were, just plodding along car was fine. Put my foot down and the K Light would come on... once on it would stay on a lot and only occasionally go out..
I changed my spark plugs and air filter the other week and its not come on since so I presume the air filter was blocked or something and when it needed the most air it couldnt get it.
Im glad its sorted but thought id post this to help others..
Minipug