there are many posts on this subject, eps. on the 300E's, one being my own. Do a search, u'll come up with a list. Heres some for starters, Dirty/clogged injectors, bad OVP Relay <~~ Check this if it's happening a lot in the warm weather. it's right behind the battery aka overload relay. Get the pic from Fastlane if you don't know what it looks like.
Good Luck