I just bought a 89 300E with a starting problem. I've searched this and other MB forums and found a ton of tips and examples for this problem but none that address my exact symptoms. A little history:
The car has 115K miles on it and appears well taken care of. The previous owner related the following: She was driving home from work about a year ago and the car started running rough and died at a stop light. She got it to restart and drove it home (aprox. 5 mi). Thereafter it would not start. An indy shop (not familiar with MBs) replaced the idle air valve with no cure of starting problem, she had the car towed home where it has sat until I bought it.
I put fresh plugs and a fuel filter in it and it started up and ran very well to my house (aprox 15mi) EXCEPT that after the initial startup and before leaving her driveway it died after about 5 min of running but restarted immediately.
When I got it to my house I started playing with it starting, killing, restarting etc. to see if I could recreate the no start problem. Sometimes it would start fine and other times it would crank but not start. I then noticed that the times it started that all the dash warning lights would light up across the board and all go out when it started. During the no start condition the only lights that lit were the SRS and CE and sometimes only the SRS. Also during the no start conditions I can hear the fuel pumps priming when the key was turned on and sometimes the car would catch for a second (I suspect from the residual pressure in the lines) but not run.
I would suspect the normal gremlins of OVP, FPR, ECU if it were not for the actions of the warning lights. Could the ignition switch be at fault ?
Any help or ideas would be greatly appreciated.

 

During the times you turn the switch to the ON position and all the lights do not come on, play with the switch and see if they all light up then. If so, it could be the ignition switch. Also, the European fuses are known to develop bad connections. Simply remove and reinstall them one by one and see if that makes any difference.

It could also be as simple as a loose wire connector somewhere. If I think about it later I will look at some wiring diagrams and see where the power from the igniton switch goes.

 

The wires at the back of the ignition tumbler could be loose. I had an issue like this before. It turned out to be a faulty temperature sensor to the ecu which was giving out false reading and sometimes the engines would just shut down and restart rough.