I ordered some new rubber hoses going to/from the idle valve. I finally found a test for the OVC relay, I don't think that's the problem, but it would be an easy fix if it was. This test (from the BenzBin web site) claims that if you have voltage at the 87 pins, then the relay is ok. Since these are the pins attached to the fuses, it's easy to test with the fuse in place. My relay tested ok. One thing I may have left out before, the voltage at the idle control valve is only 2.5 volts, both with ignition on and not running and running.

Thanks for the great advice so far, I'm sure I'll get it tracked down eventually. It really is running fine without the valve plugged in, so it's good to be able to take my time while diagnosing this.

One more possibly tied in problem, I'm not sure if my 4matic is working. Neither the warning light or the engagement light ever come on. We've had a little bit of snow up here, and I have yet to see the light come on or been in a driving situation where I could tell the front wheels were engaged. I've purposely caused the car to start sliding in a turn, and it won't come on. My tires were almost bald, but I don't think that should have had any effect on the 4 matic system (except making it engage more). I now have new tires, but haven't had any snow yet to test them in.

Dave