got a p38 2.5dt,
just changed the engine head was cracked, got it running fine eventually but have noticed when i revved it it was fine revs out no missing but when i take foot off pedal. a large hissing sound like something to do with turbo any ideas?

could be any of the hoses from the intercooler in and out right down to the turbo could be slightly loose on the clip and its sucking/releasing air pressure or could be the brake vaccum pipe