I'm not sure from your thread if all the parts you replaced were in an attempt to resolve your current problem or because they needed replacing due to other symptoms. Let me recommend that you take your 300CE to a MB-trained tech or to a local MB dealer's Service Department ... either one should be able to diagnose the cause of your rough idle and make the appropriate repair. Throwing parts at a problem is never a good idea and becomes very expensive. You don't mention replacing any vacuum lines/hoses ... I'd suspect leaks in old, dry-rotted hoses could be attributing to a rough idle.

__________________
Fred Hoelzle