Stepper motor settings & Idle target rpm

[Asho88]

So I've been researching heaps and doing a bit of trial and error but I've gotten stuck. I can't get the car to idle with out holding the throttle slightly. I figured maybe my stepper motor had died but got it idling with it set at 250 steps and quite a rich fuel which leads me to believe the more steps it does the more it opens (more air hence needing the fuel) I'm also trying to find the target idle rpm table as it hunts around a bit watching the gauges it seems its fluctuating timing. Are there any other tables I should be looking at? Been trying to make as little changes as possible but seem to be going around in circles.

Added info
253 Vn top swapped was hoping I'd just have to play with the fuel map but I complicated it by adding a cam and bigger injectors into the mix 42lb and 4502 crow cam. I plan on turboing it eventually hence the injectors and I didn't have a cam so figured why not go a bit bigger in the process.

[brindo]

Whats your idle ignition timing? And can you confirm it with a timing light?
Assuming everything else is ok, where is the throttle stop set? Can you wind that in to let a bit more air past the throttle blade and reduce the IAC stepper position? And is a PCV hooked up as if just venting to atmosphere may need a bit more throttle than normal to idle.

[Asho88]

Around 24 degrees but I was playing with it to see how it effected my idle. I did check it but can't be 100% I'll need to short the diag plug so it sets to 10 degrees and check it that way. I haven't touched the throttle stop. Pcv is hooked up. Cheers

[brindo]

Yep bridge the diagnostic port and confirm 10 deg. Idle timing of 24 deg should be fine.
Then try opening the throttle blade a bit and hopefully you can get it to idle.

[Asho88]

Yeah I’m confident it’ll idle with throttle blade adjustment but I’d like to know how to set the stepper motor up to work correctly lol

[delcowizzid]

Adjust the throttle screw until you get 10 to 20 iac steps hot idle.you will also have to restart it a couple of times if you move the idle screw very far and kick it out of idle mode key off and restart to reset zero throttle.

[Asho88]

So set it at 10-20 then adjust the throttle position to suit?

[pman92]

Wind the screw out until it idles.
Tune the fuel / spark so it's correct.

Then check IAC steps, you'll probably find you have either more than 20, or 0 and it's idling really fast.
Adjust the screw again until you have 20 steps at hot idle.

Dont stress too much about setting it perfectly until you've got the fuel and spark close, because you'll probably be coming back to adjust it again anyway

[Asho88]

So checking the steps what do you mean? Aren’t they set in the computer I was playing with them the other day so my understanding is you’d set steps then adjust idle screw. Not being a smart arse just trying to get my head around it. I always thought throttle to be 0% and stepper motor controls idle but my experience is with a haltech and mustang throttle body. Cheers

[pman92]

Yes step position is controlled by the ECU.
At ignition on the ECU drives the stepper motor all the way closed, then opens it by the "number of steps". The steps are just the increments from fully closed.

You monitor the current step position with TunerPro / scan tool or whatever, and adjust the idle screw. As you move the screw and let more in / out, the ECU will respond by moving the stepper motor to maintain the desired idle speed. You see this as the step count changing.
The goal is to adjust the screw so that the step count is about 20 (closed to fully closed, but not quite) at hot idle with no loads on.

The ECU has preset step values it defaults to when entering idle mode. By having it adjusted correctly, it enters idle mode smoothly without stalling or the idle hanging.