I have a 1987 190E 2.3 8V that has an intermittent idle
problem. It's similar to other idling problems described
in this forum but there is one thing that happens that
might be a clue to someone. If I start it up it runs fine
until it warms up to a point where I will hear a relay
click somewhere (haven't figured out which one yet) and
then the idle will go up to about 1500 RPM and then down
to about 500 and repeat. I'll drive off and it seems to
calm down until I stop for a while and then I'll hear the
relay click again and the erratic idling starts again.
Before I tear down the FI system and start testinf sensors
ect. I was wondering if anyone had been through this before and identified the problem.
Thanks,
Steve

Try to replace the overvoltage relay. IT is located behind the battery.