Join Date: Jul 2009
Location: United Kingdom
County: West Midlands
check the earth strap at the back of the cylinder head held on by a 13mm nut, right hand corner, just behind the thermostat. i've done lots of work on alfa cylinder heads in my time, i left the 13mm nut loose once by mistake and had pretty much all the sumptoms you have, sometimes the car started, sometimes not. when it started it wouldn't rev too well and was lumpy as hell.
if the nut is only finger tight, or loose, it'll cause resistance in the current flow through the earth strap, which will cause havock with the ecu as it operates by switching components... to earth! its easy to overlook this earth when reassemling a head, as i found out, but dont just grab it to see if its tight as it may "feel" ok but still not be tight enough, you'll need to actually get a socket on it and tweak it. it should be a nylock too!
hope that helps mate!