getting spn558 fmi2 code 431 which is error on low idle validation switch. Have replace throttle position sensor twice that goes on pedal. Truck will loose accelerator and go to idle for few seconds then comes back. had new coolant level sensor put in few months ago. Plug looks good and coolant is well above sensor. I don't have the break out plug to insert in apps to see what it is doing but when I unplug it and start testing each wire, with key on, I get 4.97 volts on wire c (5 volt signal wire) which is pin 22 of the ecm according to the wiring schematic that I have and no current on wires A and B pin 9 and 23 on ecm which makes sense to me. However, when I test wire D which is pin 1 of ecm (the other 5 volt signal wire) I only get 4.45 volts and I also get 4.45 volts on wire E pin 11 on ecm which doesn't makes sense to me because it is not going through the apps sensor. No current on wire F pin34 of ecm. I am new to this electronic crap so my wild, uneducated guess is something wrong with ecm. I have check the wiring best I could for chaffing , damage, etc. and everything looks ok. Is there any way to test ecm?
One thing first and you probably checked them, the grounds.