Alfa 156 gta - unhappy at idle

I recently bought an Alfa 156 gta, and got a slight problem, it doesn't seem to like idling. Hardly a surprise given how it performs at high revs (!) but let me describe the problem.........After starting it up it idles fine for a minute or so, then a warning on the info screen pops up saying motor control system failure, go to dealer. The engine warning light comes on on both the info screen and the rev counter. Then basically it idles very roughly, but other than that performs faultlessly and revs to where it should etc etc. Also the other thing I noticed is it runs very cool on the temperature gauge compared to the other Alfas I've owned (between the two lowest marks on the temp gauge). Rather than take it to a dealer does anyone have any immediate ideas? Could it just be the temp sensor?? Any suggestions gratefully recieved!!
andy