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.

you have a short in the wiring somewhere....from the sound its in one of the sensor circuits.....look for broken wire insulation around the connectors (wire)
thats where i would start.

If the check engine light is on, it should set a code. jim Forgione has a really helpful website at http://pages.prodigy.net/jforgione/MB_S500.html with a schematic of a code reader you can make for $15 or so at the bottom of his page at
http://pages.prodigy.net/jforgione/MB_X11.html

If you get the codes for the various systems, the code book can be had for free from Steve Nervig's website at http://web.mac.com/dakota/Mercedes/Indexes.html. Download his Service Library for a ton of great stuff.

Once you know the codes, you can figure out what to fix!

Gerry