ive noticed it doesnt do it when the cars cold once its warmed up say u drive somewhere and stop and then come back to the car half an hour or an hour later and start up the revs will drop to nothing then gradually move up to about 600rpm, as people said it could be a tdc sensor or somthing but i couldnt find it, ive also herd about cleaning the throttle bodies but theyre all encased and im not that good with engines. anyone shed some light onto it its really quite annoying.