Failed spark plug wires and/or ignition coils can cause intermittent misfires (rough running); the Check Engine Light may also illuminate. Diagnoses of the ignition system will be necessary to determine which components are at fault.Google+
Car Problem Reports
Mercedes-Benz E320 4MATIC Bad Spark Plug Wires/Ignition Coils May Cause Misfires and Possible CEL
Mercedes-Benz E320 4MATIC Problem
Visitor, 2000 Mercedes-Benz E320 4MATIC, 120,000 mi
In warm weather, usually on an incline my check engine light will come on and the car acts like its not running on all spark plugs. If you turn the car off and back on it's fine.