I'm not a tech and don't even want to take a stab at it.
However, since we're on the topic of idle I'd like to add an additional question here regarding idle on my 93 190 2.6:
At certain times, upon startup only, my idle will race up to 1300 or even 2200rpm and refuse to settle back until I start driving. This *only* happens when the car is warm and has been:
1) at elevated highway speeds for long period of time then shut down and re-started after a short duration (ie: fueling), or
2) if I'm re-starting (warm) after failing to fire it on the first attempt (read: let go of key too early and it died).
It's also stumbling on starter-power a little more before cleanly firing on warm starts, if that matters...
Keep in mind that this occurs infrequently after highway trips and occurs far more under scenario #2 above. Goosing the throttle rarely if ever helps re-set the idle. Only after shifting into gear and driving 1/4 mile or so will it re-adjust. I have no idea what may be causing this, besides possibly the O2 sensor or *shudder* the idle speed computer (doesn't that cost like $1700?!). My 90k service is coming up but I'd appreciate some help from those interested/knowledgeable about idle issues. Oh yeah - and it IS becoming more frequent. Ideas?