Ok so you say the black blue has 5.40 volts and the black has .08 ohms this is good . The black blue is the controller for the iac this just tells us the ecm is trying to operate the IAC.

I will give you the next two steps.

1. Spray your intake and all vac lines with brake clean. If you get to a vac line and the idle jumps up it means that vac line is leaking. Fix it.

2. Take off you IAC and look inside it for carbon sludge build up or it may just be stuck. Some time you can clean it out with what is called seafoam or sometime you just have to get a new one. Use a new throttle body gasket and IAC gasket so you do not create a vac leak and avoid taking off the throttle and cruise control cable thy are not to fun to re adjust. There are 4 bolts holding on the throttle body.There are two screws holding the IAC on and two coolant lines attached.

Let me know what you find just for all the future HANers. If you find nothing I have one odd ball idea or your IAC is stuck (if you find no sludge).

p0420 Is probably a failed cat you can get them cheaper at an exhaust shop
p1129,p1519,p0505 can all be caused by an IAC problem and or vac leak.