Thank you Paul.H and Madmadmax for your suggestions, they open a number of areas for further investigation. one point that concerns me is, the MAIN (and i mean Main) dealer told me there were no other error codes on the system; is there any merit in them telling me porkies? however i take your point about cleaning what is cleanable on the engine, My only problem with that is, as with so many C5's, the owners manual (book with any useful information in it) has gone walkies, so i am desperately trying to locate a correct one before i go wading into the engine like a gorilla. I am an engineer, and consider myself to be pretty competent, but i do like a book of words to consult now & again. one other thing that does ring bells is, the comment that Madmadmax made about pressing the gas pedal & nothing happening--------is that indicative of a particular problem? and could you possible elaborate many thanks in advance Regards Keith