canesso

I have been having idle problems with my 1991 500sl for several years now. I found quite a few threads with similar problems and I have managed to fix some of the issues but I still can't get a consistent 650 RPM idle. A smoke test revealed leaks in the rubber vacuum hoses under the air filters. I replaced all of them. The smoke test also showed that there might be a vacuum leak in the intake manifold gasket. I have removed the ICV and soaked it in thinner for 24 hours. I then tested the ICV by unplugging it while the engine was running and the idle shot up and then back down when I plugged it back in. I measured the voltage on the ICV and it never went above 4 volts. Does anyone have any ideas?