small bore pipe split or may have come off the turbo.
Hi this happened to my zafira cdti 150 i had a call out for an other issue and the AA repair man found that asmall bore pipe off the turbo had split. I dont know exactly where as he was underneeth the car not me, He replaced the last 6" with some rubber pipe as the origional was hard plastic.he knew what to look for as he had done a few he told me. It cured the problem. It happend as you described letting off throttle at low speed and then re applying the throttle there was like an engine hick up. I also had like a miss fire sometimes at part throttle My EGR was changed for that under warranty but that didnt cure it. Infact it was exactloy the same. My car had that problem still after a remap and an DPF delete too. so a chance AA call out solved it.
This will be a pig to check on alfa 159 due to the undertray having to come off! saying that if its like mine it needs to come off and all the screws / bolts greasing as Alfa dealers dont seem to have grease!
I have a full service history 72k ex fleet car serviced and stamped at local alfa dealers in flintshire and when I changed the air filter there were feathers, 1 dozen or so oak leaves, moths and other insects as well as dirt and dust galore! but had a service stamp from the alfa main dealer 1,200 miles earlyer ?? strange thing is that was february 2011 and the leaves fall in the autum ?? the car was on the indoors for 8 weeks from where i bought ??
there is lots of surface rust underneeth on suspension parts on my car too, will have to sort out and treat it asap.
Anyway sorry to rattle on hope the info on the pipe might help.