had the punto 55sx since new my parents have passed it on to me and its had a few problems in the last year i have been drivin it ie. (replaced the head gasket, starter motor etc). Anyway recently if im going at speed on the motorway usually over 70mph 4,000 revs the car starts to make a hissing noise and looses all power.. i have to pull over onto the hard shoulder and restart the car... and then its perfectly fine again. anyone know what the problem is?? any help would be greatly appreciated