A 1988 300E stumbles badly every time the check engine light comes on. Light comes on at any speed and any engine temperature. It usually pulses for a second or less but sometimes will flicker for several seconds. If it stays on the engine ceases to run. It will always restart after it kills. I have replaced the fuel relay, overload protection relay, oxygen sensor, and fuel filter since the symptoms developed one month ago. What else turns the check engine light on besides the O2 sensor? The engine has a CIS-E fuel delivery system. When it runs without a light it runs very smoothly except at prolonged idle where it will start to miss after 3-4 minutes of idling.