i know this is a trivial suggestion, but when you switch from economy to sport mode, other than the lever selection, does any light come on in the cluster panel, like it does in the japanese cars ? or is the switch the only thing to go by ? could it be the case that the switch has stopped working and even though you've put it back on the economy position, it is still in the sport mode ? I'm asking because you mentioned that now the car still has more acceleration from stop now. i'm assuming it wasnt like this when you were running in econo mode ?
just a suggestion...