i have a 2003 st170 when i start it from cold the revs stay at 2k for about 15 mins till it warms up it takes ages for the choke to cut of,even if left for 10 mins to cool down the choke seems to kick in all the time,when warm its ok but if i go on the motorway for a run when i come of the revs stay at over 1k for about 5 mins,does anyone no whats causeing the problem as its like the car drives itself for the first 15 mins any help.thanks ste