[merc Dod]

The tach just drops and regains but what I thought was an unrelated problem (the car maybe twice a week will suddenly jerk or shudder. I thought it might be a transmission problem. Could it be related? I assume the ICM is the rectanglar object that the spark plug wires originate from. Is this correct? If so do I somehow dissconnect a plug and spray it down inside with contact cleaner. Is that the best procedure?