Id try getting a second hand throttle body and trying that..
eBay is your best bet (thats where I got mine), there are quite a few people on there breaking 145's and 146's (they are basically the same car)...
I have heard Autolusso (I think its spelt right) is very good for spare parts, if no luck on ebay (cheapest option), then try Autolusso -
Auto Lusso - Quality Alfa Romeo Servicing and Repairs
If that doesnt work id try a new air mass meter
Either way, replacing these two parts is alot cheaper than getting a diagnostic..plus then you have to buy the replacement parts on top! I think one guy on here said he spent like £200 getting sorted what cost me £7.50!