As I understand it, the IAC steps range from 0-255. Park position is set at 160 steps. From a data log, I can see that it is indeed at 160 steps at start up. The car starts, idles high for a second or two, then I see the IAC steps coming down in order to lower the rpm to a commanded 1200 (during warm up). Then, once the rpms drop below 1200, the steps start to come back up. It is not enough steps going up though, as the rpms continue to drop below 1200 (and keep dropping). The IAC steps NEVER go above 160 to bring the rpm back up. Why wouldn't it go above 160 to bring up the rpm to the commanded 1200?

FWIW, at warm idle, IAC is around 65 steps. I know it's a little high, but it shouldn't have anything to do with the issue, should it?

Thanks!
Dan

 

Are you running 32B? Seems I remember 32B having a table that is IAC counts vs. coolant.

 

Dan,

The factory and some aftermarket throttle bodies have a hole drilled in between the blades to alow for more air to pass at a lower iac count. Holley does not have this hole, 100% of the air at idle goes though the tight iac passage which requirs a larger or higher iac count to accomidate for. I have a Holley and my values are high but I have never had an issue with it yet.

 

I'm running $6E. In Tuner Pro, I don't see a table that would limit the max steps of the IAC (and I'm using an .XDF file that has a lot more IAC parameters). Maybe it's worth a try to raise the park position from 160 to something like 190?

Thanks for the info! I was thinking that the higher IAC count at warm idle wasn't the cause of the issue; glad to hear it is ok for you.

 

That's news to me. I was always under the impression that 160 steps is the highest the IAC will go.

 

The reason is you're lean, though, probably. IAC shouldn't need to be 160 to hold a 1200 RPM cool idle. Increase the Open Loop % Change vs Coolant Temp, and maybe add some Afterstart Fuel (but only after you're satisfied with the warmup mixture, and if the startup is losing RPMs for a few seconds).
Since it's surging (from your logs) it's safe to add 5-10%.

One thing you can do is wire up your wideband to a spare battery, like a lawnmower or motorcycle battery, and record the A/F during cranking, startup, and warmup without having to wait for the unit to warm up.

 

At location $572 is the MAX IAC Steps parameter (for the $6E mask). That value defines the highest possible IAC step count. Most likely it is set to 160, which is default for ARAP.

RBob.

 

Yup - definitely too lean during warm up! I richened it up by 10% through 140* F last night. Thanks for taking a look at those data logs!!

Thanks RBob! That must be the same as the "IAC park position" in APYP, because I raised it to 190 last night and the IAC steps finally went above 160 to hit my target idle. That, along with the AFR % increase has just about solved the issue.

 

I've added this into my tunerpro $6E definition file for anyone else who might want to adjust this. Link: http://home.insightbb.com/~rhuarc/links/index.htm

 

 

I'm using E6 but I guess I'm lost...Why are you trying to go above 160 counts at idle? The ecm wont consider 160 counts as an idle at all...hence your windmill effect. I think the 60 counts your seeing at idle is a big part of your problem. IIWY I would warm up the motor and set the counts for around 10 or even less...reset your IAC and go from there...60 counts at idle is way too high in my opinion.