code po753 on skoda roomster SKODA ROOMSTER (5J)

Hi to everyone i have just purchased a Skoda Roomster 1.6 petrol automatic,and it is giving a fault code of po753,the problem is that the car is intermittent with its fault,one minute ok then into limp mode,the symptoms are the gears change with speed and show the gear you are in on the dashboard no problem,then after a few miles drops into limp mode,and wont go over 3rd gear,why is it that if there was a serious problem the car drives fine,so im thinking its no mechanical could anyone tell me what are the causes of the code,so i can start eliminating probable causes,thankyou in advance to anyone who can help.