severe lack of power?

i have a 56 plate 35s12 2.3hpi
on a cold start the engine will start but on pressing the accelerator very little happens. if you leave it running 5 mins and then press accelerator there is more of a response. while driving it really lacks power especially up hill. steep hills is a 1st gear job at 10 mph. motorway hills are generally taken at 40mph. not good. a couple of days ago i had about 5 miles of a normal van, lots of power even uphill, then it went back to low power. the yellow engine light comes on frequently along with the flashing red edc light. sometimes the edc light stays on. i have changed the airflow meter but no difference. gonna take egr valve off today + give it a clean. any advice would be most welcome. thanks