Yes, I understand what you saying Wicked, and but I am really tight in time right now. work, college, and just going to a trip.
So I really want to try to see if a shorter method will work. I just want to eliminate the RPM SPIKE for now. so if only need to mod the megasquirt unit itself, then I can do it in an hr. but if I need to rewire the car, and do this and that, then, it will take me alot more time!

So what I basically want to try is, can I try a portion of your mod?

Like just performa the MS unit mod. (OptoOut -> VrIn -> VrOutInv -> Tsel) But leave the car side of the mod. (wiring, fully standalone, etc). So I just have the CPS fully connected to the stock ECU. Just tap the signal cable to the MS. and so this way, I can have my Stock ECU control the IAC.

The only REASON I don't want to go full Standalone yet, is because of the IAC (idling issue) and the amount of time I have now.
I will try to find a way to get that working without stock ECU later on. (maybe after Xmas) but for now, I want to keep my stock ECU.

So from your experience.
Do you think on what I want to do will eliminate the RPM SPIKE? or you know as a fact (or tried) that the RPM spike will still be there?
Like I just change OptoOut -> VrIn -> VrOutInv -> Tsel, and tune the two pots. Will just doing this will eliminate the RPM SPIKE?

Thanks!