I had the same problem last year, i'd have to sit with my foot on the gas for nearly a minute before the car would idle on it's own. I checked all the plugs and it turned out that the furthest one away from the front of the car wasn't working.Not suprising because it's the hardest one to get at.Same with a friend of mines 300sd.This helped but not untill i changed out all of the injectorts did i have a flawless start. My suggestion would be to start out with some diesel purge before changing the injectors though. There is a product that you introduce into the line that goes into the large fuel filter from the injection pump .You place that line and the return line in the bottle and run it through your engine till it runs out.I believe it's called lubro-moly.Apparently hard to find but well worth the search.