In other words, since my idle went down upon MAX A/C is engaged, it points to a bad TPS or ICU.

Since my idle is already high, do you expect it to go even higher once I pull the TPS? I have just got myself a digital multimeter. I guess I could measure the resistance "between the middle pin and the pin furthest from the CSI (cold start injector)" when car is not running. If the TPS is good, I should get 0 ohms.

One more question about TPS. Would it be the cable that is bad? When I was at one of these parts web sites, I saw a "throttle switch" and it looks just like a cable.

I guess high idle is one of the most common problems for W126 cars. I hope this discussion will benefit many otehrs. You are a great help. Thank you very much.