Thanks a lot, bobterry99. I have some update to my car and hope you don't mind to read it as it's a bit long for telling what's going on in the last couple days.
I sent my car to one local garage who is familiar with electronic problems on Monday. He used the Mercedes Diagnostic tool somewhat similar to the right cube shape component in the picture and connected with an IBM T30 laptop. He confirmed that the replacement CC amp bought from the autowreck was for W140. I've taken some pictures and highlighted some differences. He told me some IC chips on my original CC amp was blown and he was trying to transplant some switchable IC chips from the W140 to mine and rewrite the codes/programmes inside the chips. As my knowledge about electronics is only up to V=IR, I feel it was amazing. Last night I went to the garage and he told me he found out some chips from W140 was not good at all. He said the W140 CC amp was also a faulty one but someone has put a very thin wire to by pass certain circuit to suppress the idle surge!
He has also called a friend who drove the same MY94 SL320 with the identical CC amp parts no. 1295451932 (I didn't see the car physically but he showed me a text file copied from the chips of that car with the parts no.) to come to his garage for doing some test the day before. He installed his friend's CC amp into my car but he said the idle was still high but his friend's car was ok with that CC amp.
He then suspected it might be something wrong with wire harness from the ETA socket to the CC amp but he said the wire harness was ok after inspecting with voltage meter.
My question is:
1)is there any coding input or remapping required whenever installing the new throttle actuator or CC amp?
2) Though the electronic throttle actuator was a brand new one, should I ask my mechanics to do the switch for both ETA and CC amp from his friend's car again? If my car is ok with another car's ETA, can I say I have a faulty ETA though it's brand new???
3) Though it's a 1994 vehicle, does it have any self learning function that it has already 'learnt' W140 behaviour so it didn't comply with another good R129 CC amp?
I guess these are weir questions but they have been stucked in my brain for days. I'm very depressed now as I've already spent quite a lot of money on buying the brand new ETA and the cheating W140 CC amp but my car is still sick. I've also contacted the 2 ECU repair specialist mentioned before but they both said they don't have experience in repairing this unit. I hope you can give me some advice or any suggestion for identifying the problem are very much appreciated.