I think it's 99% the MAF sensor, as I had the same problem last year. I checked all other options first, but at the time I knew that v6 MAF sensors were about £190. With some digging I found out that the 2.5 v6 MAF sensor is exactly the same part number as the one for a Vauxhall Astra, but the Astra one only cost me £58. All you need to do is pop to a local auto factors and ask for a bosch MAF sensor for the Vauxhall, part number I can supply in a couple of days for you, as I'm away in Spain testing at the moment.
Once you have the Vauxhall sensor, remove the new sensor from the tube and replace it in the alfa MAF tube. Also you need a tamper proof T20 Torx bit i think to remove the sensor from the tube.
Believe me, once you have the new sensor, check the part numbers, and you will see they are exactly the same on the sensors, the number on the MAF tube will be different, but that does'nt matter as you will only be swapping the sensor. Also do a ECU reset before driving. Then hopefully everything will be fine again, as mine was.
Hope this helps
Prototype Development Technician
McLaren Technology Centre
Last edited by yeosport; 08-04-11 at 00:32.