2.0 tdci problems

Hello new here I'm hoping someone can help . I have a 2010 focus 2.0 tdci with 153000 miles full service history uses very little oil . I'm having a problem mainly when cold intermittently when warm which is when pulling out of junctions the revs are dying no power then picks up and runs fine , the mpg is also dropping since its been playing up . It had a new egr valve and intercooler pipe in march and recently a new air mass sensor . The garage that fitted the egr valve at the time found a pipe that they thought was being crimped when the engine was moving under load but never actually told which pipe it was and they are now not being very helpful , I've checked for codes and none have been logged  any help would be appreciated .