90 miata, MS1, V3.0, hi res firmware, using the 90-93 MSPNP IAC settings.

i bought the IAC mod kit from DIYautotune. kinda rushed through the install not paying enough attention. big suprise, the IAC didn't work. started looking for the issue, i am getting 12v at the white/red wire at the IAC, so that it good. the wire going from MS to the IAC is good. the TIP transistor is ran to Q4. the diode is running from the middle leg of the transistor to s13(IIRC) on the board, banded side towards the board. i went to double check the wiring and i noticed i had pin 1 and 3 on the TIP transistor reversed. i also forgot to pull resistor D8, but i actually caught that after the first time it wouldn't work, so it was just left in for the first few minutes.

i have plugged in another IAC and no change. if you hook power and ground to the IAC it moves all the way to the opposite side, so the valves are both good. so in short, what did i burn up on the megasquirt? i was planning on going to radioshack and trying to pick up a new transistor and diode and trying again. nothing "looks" burned on the board, and everything else still works fine.

 

no one? well i will replace the transistor this weekend and report back.

 

Can you get the idle LED to brighten and dim on the Stim with this?

 

i don't have a stim matt.

 

i replaced the transistor today and still no working IAC.

 

pic of how you built it.

 

it looks exactly like this. pic from the miata turbo wiki

 

just went out with a multimeter. full 12v at the red/white wire. there is .12v between the 2 IAC wires.

i do remember with the old transistor i actually had .9v at the blue and orange wire for some reason.

is there anywhere else i can run the IAC circuit beside Q4?

 

In that case, please test the signal on pin 1 and 2 of the TIP122 with your oscilloscope on the car.

 

Maybe you shored the solder pads at Q4.
If you have a multimeter, try a diode check between the pins.

 

i dont have a oscillscope, just a multimeter. i am really thinking i messed up q4 somehow. i need a new tip on my iron, so it was a real pain to get it soldered on the board.

 

just checked for voltage at the transistor. pin 1 and pin 3 both have 0 volts, and pin 2 has 12 volts.

 

Do you have a mica insulator between the transistor and the heat sink?

 

yep, and the white grease on both sides of it too. i am using the nylon bolt and nut also.

 

Then are you convinced that the IAC itself is actually working? I know mine doesnt...

 

Yes. I tried 2 different ones. And if you put a 12v and ground to it it snaps all the way open.

 

so can a run it somewhere else besides Q4? i remember seeing a pin-out for the main chip before, but i can not seem to find it again.