| My 999 did this a couple of times in the colder damper weather over the winter. It was usually after a gentle cruise on the motorway and manifested itself as a racing engine when coming to a halt (you had to pull the clutch in to avoid going up the back of the car in front) or like having a cruise control that couldn't be turned off. It would stick at about 5000 rpm.
It was somewhat disconcerting to say the least.
I pulled everything apart but couldn't find any reason for it. As weather got warmer (and drier) the problem disappeared. I can only put it down to some kind of icing up - maybe in the throttle cable somewhere or the throttle butterflies or sensors - some dampness that intermittently froze up. A brief halt and engine stop and restart always cleared it up. |