MSefi.com read only forum (Jan.15,2018)

MSII, 2.68 code, V3 board with TIP120 mod

IAC was working as designed and had been working great for over a week. I warmed my Jeep this A.M. and the idle droped down to 700, got about 1 mile from home and the idle went to 2500 RPMs.

I understand there is a lot of variables here but is it common for that transistor to short out? Disconnected the IAC and the engine ran fine, logged into the ECU with MegaTune and changed the tables around (-40 to 160 and back) but there is no change. The IAC does not seem to be responding.

Some threads on this board explain that the frequency could cause it to stick open (pretty sure mine is set to 80)??

Thanks.

Most Ford IAC valves seem to run at around 300 hZ. Also check to see if the TIP120 is shorted out on a Stim.

I did not install the flyback diode, whoops. Looks like I got a voltage spike and it took out the transistor. Next step is to measure the resistance between collector and emmiter. Willing to bet it is shorted though. Hope I bought two when I ordered them from digikey!

Changed out the transistor and installed the correct diode. Changed the frequency to 320Hz and the system is still acting the same. More troubleshooting.

Got it fixed, there was a short from the collector to base leg of the transistor down where Q4 was supposed to go. Apparently when I extended the wires they were far enough apart to work but as I drove the rig they vibrated and created the short. I moved the collector wire to the other (towards DB37) end of R39 to have one less wire on Q4.