MS3 or MS3X for IAC?
 

Stupid Noob Question:

I'm slogging my way through wiring a MS3/MS3X from DIY Autotune into my "99 with an 04 MSM drivetrain" project, and I'm unsure if I should be using the MS3 "pwm" pin or the MS3X's "Idle" pin? Is there any advantage (functionally) to using one over the other? My reptile brain says use the MS3 pin to save the MS3X's pin for some possible future use. Is that correct?

Thanks in advance-

there's no need to save space on the expander, just use the circuit on that board, otherwise you'll have to built the same exact circuit on your mainboard for no reason.

My MS3/X came already built from DIY Autotune, so I presume that circuit is already built on the main board, hence my thought to use the MS3 for the IAC and save the reconfigurable "spare output" on the MS3X for some other use. Does that make sense?

(BTW, lol at "building the circuit".. My electronics skills were taxed at just soldering the pins on the DIYBOB!)

As Brain said, there's more than enough free outputs on the expander. You'll never use them all, so just use the expander idle output. Don't forget to add a 1N4001 diode with the banded side to 12V and the other side to the idle output (shouldn't DIY already have done it, not sure if they do).

You can use either, you choice.

this assumes the PWM circuit is built by you guys already. If this is the case, do you already add in the flyback diode on the tip120?

If yes and yes, then I'd the mainboard's (FIDLE) over the expander's circuit (IDLE).