My 1990 300E M103 is intermittently idling fast on inital startup when the engine is warm. If I kick the accelerator pedal it will come back down although I don't think it's a linkage hangup. Could it be the idle control valve?

If tapping the accelerator pedal brings the rpms down, I'd suspect linkage. This needs to be cleaned and lubed periodically. I've read in numerous places to use transmission fluid to lube the linkage with after you've cleaned it.

initial start up should be fast and high. after 2-3 mins.
rpm should drop where it should be at 700.

For peace of mind, it's easy to remove your idle control valve, spray it out liberally with carb cleaner and blow it dry with compressed air. Once dry, a shot or two of WD-40 is a good idea. Reinstall and forget about it.