I have a 05 transporter (375000km, auto) that was clunking between gears, (assuming valve box) now after a 'sharp breaking incedent ' where I initially lost power, upon gear changes the van will surge aggressively and then cut out. When trying to restart the van it can be hard but normal start up is fine. First thought was loose battery terminal but all seems to be tight and stable. Van will idel fine and revs well while in park. Any help/ suggestions would be great