You have to be very careful about this diagnosis. There's a very 'powerful' emporium just west of London who (some might say) developed a fairly uncanny 'knack' of making just such a diagnosis of this to justify a 'we can fix it but we'll have to put one of our chips in it /£175 pounds to you Sir approach'. Students of Fast Ford magazine will remember that they also trotted out that one to the journalist that took FF's project S2 there Last year.
If anyone does own an S2 and their tuner offers to 'rectify a fault' using the above old chestnut, at the very least get a second opion/ideally go and see
Jamie at Jamsport.