Could be a few things but first thing I would check the air flow meter between the air filter and manifold to engine, disconnect the wiring to the air flow meter and go for a run if it is this (common fault) there about £80/100 failing this a diagnostic test.Also catalitic converter can sometimes break up and block the Exhaust (usually notice a rattle from underneath) Hope this helps.
Nigel
May 2012
howtomendit.com for free repair help, information and advice.
