This thing has been pissing me off for awhile now. I've tested the IAC valve and get 12.8ohm, applied 12V and the valve closes. I checked for continuity from the plug all the way to the middle leg on the TIP120, and checked to make sure there was 12V on the red/white wire. I've replaced the TIP120, checked leads and checked for what I know could have been possible problems with the wiring on the board. The thing just does not seem to work. Could it be the output pin on the chip? I've used a bunch of different recommended values and changed the DC to see if the idle would change and nothing. I have verified with the realtime display that the DC should be changing. I'm hoping I'm just missing something stupid. I haven't come across any other problems other than IAC.

Here are the images of my board:

 

I dont see a flyback diode on the TIP120 that wont be helping. But it shouldn't stop it from working altogether

 

Flyback diode is on there. It's connected to the middle wire on the TIP120 and S12. It's a little blurry in that pic.

 

Damn, so no one has any ideas of things to try? This is killing me.

 

i could never get mine working either... i just adjusted the idle with the bypass screw and ignore the fact that it idles at 1400 rpm sometimes :/

 

I got up some motivation to try fixing this again. I'm wondering if the output pin is fried from me not having the PWM circuit together correctly before, so I did some research and found the pin to be PTA1/pin34. I'd like to test it, but is there really any way to check without a scope? I'm thinking if it's bad, I can just modify the code to use output2 and recompile. We don't use output2 for anything, right? It's just for unused tach output? That's the only easy one to modify since it's still on port a. If I have to choose another pin, I have to change ports which requires rewriting all the areas for idle to use the new port. output2 is easy since I can just swap the definitions in the header file.