Your senario strikes me as more than a little odd. The easier starts are understandable. Once those glow plugs cycle out all is restored as with your old glow plugs. So what concievably could have kicked the idle up?

The only viariable I can really think of is you hit or bent something on the pump when removing and installing the glow plugs? That is unlikely. Or if it is an oddity with the plug change others should have mentioned it. Might want to check the archives. I really do not expect you will find anything though.

About the only other speculation is the intense new heat of the plugs might have had an effect somehow on the prechamber carbon and soot build up. See if your fuel milage is noticably better as well.

I have been watching for a couple of years now. Still unable to find out why some 240ds get around 30 mpg while a lot are lower to mid twenties. I feel when these cars where new they may have all gotten much more simular milage than they seem to get today. I suspect whatever is causing it is a common but unrecognized fault.