My 99 SVT (now at 102,000km) has had this problem off-and-on since around maybe 50,000km. After many trips to the dealer, the one fix that seems to work is giving the throttle body a good cleaning. That usually lasts for 20-25,000km, then it starts doing it again - just now and then at first, but within a week or two, it does it almost all the time.
Symptoms are high idle at a stop....drops to about 2000 pm, then s-l-o-w-l-y settles to around 1300. When driving, it's like a really, really bad case of throttle hang.
