My mate was out test driving an R33 Series1 Skyline and giving a little bit to see how it went but when it got to 6grand the car cut out and the revs would drop untill he took his foot completely off the throttle and then back on again... It did this everytime, he left his foot on it one time and the car droped to about 3,500rpm and was still droping... The car was completely stock and just imported, it had bout 80,000km on it. Any idea whats causing this would be helpful.