I just bought a 1989 300ce which has an idle problem. Every once in a while the engine dies when idling or slowing down. When the car dies I see both the check engine light and ABS light come on (a second before the engine stops). Car starts right up but in order to keep it from stalling I have to keep my foot on the gas. The rpm drop is very sudden, but sometimes the computer can recover from the stall (RPM goes to almost 'zero' and then go back up). The idle is not very smooth either. Every few seconds I can feel a slight vibration (rough idle). It is minimal but noticable... Thank you for any help.......

Wow, sounds identical to mine, except the abs light does not come on. From what I've been reading seems like yours may be related to the Overage relay. That's going to be one of the first things I replace.
Please keep this thread updated and let us know how everything works out for you.

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1986 560 SEC *Sold* < Big Mistake I miss my baby!
1988 300SE *Sold*
1989 300CE - current car, but not for too long

My 1989 300ce has the same symptoms as well. I never had a chance to deal with it yet, because my transmission blew. Once I replace the transmission, that is next on my list. I did buy a new Optima battery that I installed. Also, I bought a new distributor cap and I'm going to buy the rotor and wires soon and see if that has an affect. I know my distributor cap that's in the car is not that good.

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1989 300CE Astralsilber/Schwarz
1992 300CE Schwarz/Schwarz

The following recent thread should give you some insight into your problem:

OVP relay whys and wherefores

Duke

Thanks guys for all the help. I am almost certain it is a faulty OVP relay. Found a temporary solution to the problem. The electronic part that kills the engine is the idle control valve. I have disconnected it. The vehicle does not stall any more and runs like a dream.

There is however a drawback. The idle control valve compensates for any load on the engine when idling such as running the A/C. You may have noticed that when you turn on the A/C the vehicle RPM goes up. By disconnecting the idle control valve my engine RPM drops (when the A/C is turned on) to about 500 RPM.