1999 Vauxhall Corsa 47,812 miles

hi
recently my corsa is sluggish as if pulling back & engine electronic light comes on it goes out straight away, but when foot is on accelerator to the floor normally going up hill the light comes on again i,ve noticed that when i bring accelerator up again it runs fine, so far i,ve payed £300 to a garage to sort this & still its doing it, any help would be appreciated