hi tony, just joined the site to try and cure your exact problem, i just bought a 2.2dti 02 on tuesday and the girlfriend drove it home from essex(230ml). it seemed heavy and sluggish on test drive but because i have not drove one b4 seemed ok. gave it a dam good clean and took the air filter out last night as it was a bit dirty, left it out and made the small drive to town today to tax it and get the new filter.
as soon as i drove from home the car wouldnt pull and felt wheezy, eng managment light going on/off as i rev. (shit). hoped it was over compensating for no filter so got home and put the filter in,,,, same (oh shit). spent 2hrs looking around the airbox incase i had disturbed a pipe but no. went through all your posts then went out again to lift the air box out to look again.(bare with it).
undone the 1st rubber hose between the airbox and turbo....a 5" leaf dropped out which had been flat over the inlet gauze(blocking it by abt 70%)................hose back on in 5 mins ,, drove the car and it flew!.
hoping you have not removed this hose yet and you have the same prob. sorry to go on but it was a "wtf" moment.
good luck