Not a fan of the IAC...

[3400-95-Modified]

So yeah I'm not a huge fan of the IAC setup in my car and the way it responds idle wise and such. Its a very floating idle and if you rev it the car doesn't snap back down to idle, it will sometimes drop down too far then try to recover and rev high then settle off, or just outright stall out.

Now my question is, would that be a tune issue, or just related to my cam and the IAC trying to recover and not working quite well... Or is it just how the IAC will respond period on a modified motor?

I'm asking before I try pulling and plugging that port and just setting my idle via a set screw on the throttle blade.

Any input is appreciated before I dig into this and create more of a headache.

[dskopek]

I have the same problem with my setup, i have a ok idle now but it will hunt sometimes. I ran without the IAC for a while and had a good steady idle and responce but had problems with the cold start and idle until it warmed up. I hooked the IAC back up and am trying to find a sweet spot for it to run in. I am running a megasquirt setup on the motor and tranny and i can adjust the step size of the IAC and that seems to be working for me at this time. I am running a turbo on a 3.4, 8.6:1 CR, custom cam with 230 deg duration and .570 lift on a 112LSA. The motor will pull 13-14 inches of vacuum at 950RPM idle.

[3400-95-Modified]

I figured cold start would be an issue, but this car doesn't see much of that. Its parked all winter and I don't drive it too far into the fall... SO I don't think its something I can't babysit for a few seconds to ensure it will idle.

I don't have much vac at idle due to my cam, but I'd have to check on that one, and I'm running DHP with a 97 ECU I can also use tiny tuner so I do have access to a lot of the IAC settings, but I don't know which ones are causing my issues.

[Superdave]

in OBD1 you can just adjust the IAC throttle follower table to fix that. I had to mess with it quite a bit to dial mine in.

[3400-95-Modified]

That doesn't seem to be a table available to me in tiny tuner... I'm gonna check a few other bins to see if it even exits in OBDII or if they used a different method to replace that one table.

[3400-95-Modified]

I guess another question to ask is, Has anyone flowed these 65mm TB's to determine how much air per IAC step is allowed through? I noticed I have a value for that I can edit and I can only assume that these TB's flow more per step than the stock ones did just due to the size of the IAC port and design of it. But I could be wrong.

[Azrael]

Is there a "time between steps" setting you could increase? It would take longer for idle speed to change but should prevent it from oscillating from overcorrection.

[3400-95-Modified]

This is whats avilable, let me know if you think any of it could help and I'll let you know what values exist there currently.

[Barry]

I would try to stay away from the throttle plate screw if I were you. I use that for my idle, and its annoying. It works great actually, even for cold starts it idles fine, but if you get off the gas too fast it may stumble and die when cold. Same goes for when its hot and the A/C is on, that extra load on it causes it to stall if you let off too fast.

I can raise the idle to 900-1000 to prevent the stalling but thats annoying and sounds stupid, also reduces my engine braking some.

I wish I knew how the IAC on my nissan works. All it gets is 12v+ and ground and it holds a perfect idle all the time and is easily adjustable with a screw.

Edit:
Rev to drive anticipate steps from vehicle speed. Wow. Theres a lot more algorithim that goes into stock idle control than I ever knew.

[SappySE107]

our OBD2 support still has some holes in it, and the IAC is one of them. OBD1 is much easier to adjust for throttle follower, max iac position, start up IAC position, etc. My wagon starts up and goes to 1100 and back to 800 instantly. I love it You can't really do anything with OBD2 other than the really new stuff, since its drive by wire.

It could be the tune though for some it. Spark timing can be retarded but an IAC will still override that with airflow if its bad enough.

Tuning is everything, and an aftermarket controller is probably where its at for some of these OBD2 builds.

[Barry]

My car cranks, revs to 1100/1200 then immediatly idles down to 800 with a blocked off IAC port. Its all done with after start enrichment.

[TGP37]

Assuming you can read/flash your cars PCM and If you can obtain your cars PCM file in BIN format, you can alter your IAC responsiveness somewhat.

Use Tiny Tuners.......if your OSID isn't supported, there are ways around that with the data base file. Easy to edit.

In the PCM file opened by TT there are a slew of tables pertaining to the IAC. Some I edit more than others are Throttle Follower settings.

Most settings are in the Accesories > IAC area, but two important ones are also listed in Uncatagorized which are.......

Throttle Follower Disable Delay vs Gear
Throttle Follower Disable Filter Time Constant vs Gear

Working your way through these settings and some trial and error, you'll find the right IAC settings for your ride.

[3400-95-Modified]

Assuming you can read/flash your cars PCM and If you can obtain your cars PCM file in BIN format, you can alter your IAC responsiveness somewhat.

Use Tiny Tuners.......if your OSID isn't supported, there are ways around that with the data base file. Easy to edit.

In the PCM file opened by TT there are a slew of tables pertaining to the IAC. Some I edit more than others are Throttle Follower settings.

Most settings are in the Accesories > IAC area, but two important ones are also listed in Uncatagorized which are.......

Throttle Follower Disable Delay vs Gear
Throttle Follower Disable Filter Time Constant vs Gear

Working your way through these settings and some trial and error, you'll find the right IAC settings for your ride.

[ATTACH=CONFIG]5995[/ATTACH]

Go back 4 posts and look at the image I posted.

[geldartb]

looked through mine and the only one i have is the throttle follower gain factor vs vehicle speed none of the ones listed under the Uncategorized area, not much listed under that on my bin.

might try playing with that one on mine since i have a similar issue like Jon has. mine does it when it downshifts from 2 to 1 but that's more of a blip but it sounds like it almost stalls but bounces back, but that's part of the problem. sometimes it will start up fine but then others i have to feather the gas to keep it alive since the idle likes to bounce when it starts.

[Alxsmt]

my idle has never been right also. floats around a little bit. my idle is also at 1200, my cam isnt huge but it does help it stay steady. my tune was never completly finished but I just assumed thats about as good of an idle tuner pro is capable of