most mondeo's  of this year have this problem  1.8  and 2.0  i work for ford  and have run  a   02  1.8  which did the same  it  would appear that the more miles that they have done the worse  they are  first place to check is  your cat  is it getting blocked put your hand over tail pipe with a  glove on  with someone  revving  the engine for you  should blow your hand away  if all is ok
                 old x19
                
 April 2008