Have had my 02 GTI running really well for past 3-4 weeks, i have cleaned the carbs replaced a bad gasket in the carbs and replaced an exhaust gasket, all was well till today. It ran fine at 1st then as the day progressed it started surging. Lots of power/speed to a loss of power/speed back to lots of power/speed and back again. Feels like its missing, so i replaced the plugs but this did not help. Any suggestions? Previous problem of bogging down but has run great the past 3-4 weeks