Shudder on accelaration comes and goes

Hi, there I've just recently bought the car listed above active sport 8v. I was told that it had been stood for two months because the MOT had ran out. On bringing it home at first everything was a bit stiff, ie: suspension gear box but loosened up on the drive after about an hour, there was no shuddering on acceleration at all throughout the whole journey. When I've got it home the three days later I managed to get it booked in for a MOT it failed on two rear shockers and one wheel bearing, so I got them fix then it was passed. Three days later for no reason its starts stuttering on acceleration at different speeds, When I say stuttering I mean as If it's loosing power and then getting it back sometimes the engine management light comes on, on the dash then goes and it's fine again then it can go for hours then starts again. I've put some redx in with fuel and it is still doing it but not as bad. Has anyone got any ideas what the problem could be?