I would like to start by saying that I have used the search button and read many pages of post about knock sensors.
A couple of questions still remain.
My car is a 1995 SL 500. I have pulled codes with a Trisco Palm Scanner.
DI....Code 05...knock sensor 1&2 faulty
EA/CC/ISC...Code 224...Idle Speed Control Switch...S/29/3 Faulty.

I understand that there is a great chance that I need to replace the ETA. The Code 224 will not stay reset. Turn of the key and its back. According to Frank's home page its another confirmation the ETA is bad.

Now the real question. Does a faulty knock sensor have a default setting when it is inoperable? Will a faulty sensor just pull the maximum timing even if there is no predetonation taking place? Should I come from below or topside to replace the knock senors? Every sensor I have read about was replaced while the engine was removed for other work!!!

Reason that I ask is because I will be dropping a chunk of money for the ETA and would like to wait before replacing the knock sensors but no if it is going to negate the benefits of the new ETA.
Thanks,
Matthew