PWM Idle Control Problem

[roflcopter]

Hey everyone...

I've been trying to pick away at all the 'little' issues I've been having while waiting on the new transmission so I can get back to serious tuning, I still haven't worked out the Overrun settings issue but this is issue number two on my list.

Basically, PWM Idle won't work. It worked for a little while, then failed. I figured it was the valve itself because I didn't have it pulling from the intake and thought that putting boost through it backwards might have been the issue and physically caused it to fail. Turns out that's not the case, I now have an assortment of Bosch 2-wire valves and all of them behave identically. Before they would instantly go full open as if the Duty Cycle was set to 100% at all times resulting in an idle around 3500rpm. I put in a new valve and made it so it pulls from the charge piping to keep any reverse pressure from causing an issue and it worked for an evening. The next morning it went back to not working anymore and reverted to full open all the time. I then checked the wiring harness and it checked out with no obvious shorts anywhere. The diode in the harness is still working properly, OL one way, ~.6V the other when testing. When testing the pins in the connector I get 12V on the power side and ~20mV on the Fidle side. I noticed that when plugging the serial cable into the laptop it would cause the valve to make noise so upon further inspection it showed that it would be closed without the laptop hooded up, and full open when it was. I decided to resolder and replace the TIP120 at this point just in case, after doing this nothing works at all, valve is always full closed. Now I can't get anything to work even though all the traces test correctly on the board and the supply voltage is good and in TunerStudio it says it's commanding whatever I tell it.

I'm honestly pretty fed up with most of this, I feel like I've checked all of the obvious things as well as most of the less obvious ones but I was hoping maybe one of you had run into a similar issue.

Thanks in advance!

[Matt Cramer]

Make sure the tab on the TIP120 is not shorted to the case or other ground point.

[roflcopter]

I had gone through all of that last night and everything checked out correctly but still nothing working.

Hopped in the car this morning and figured I'd give it a go before unplugging the IAC again and it worked fine. Drove all day with it working correctly... we'll see when/if it comes back up and do some more troubleshooting then!