OK, so school me on IAC's and how they're operated in a 730/8D/AUJP based-system. I need to know if there is a way to pull the IAC and and force it to open & close through a range of motion via TunerproRT and an APU1. I want/need to verify (i.e., see with my eyes) that I have the thing wired up correctly, and narrow down how many counts I need to close the IAC port completely. I've got something of a bastardized system, but it SHOULD all work. At least that's what I keep telling myself. Background: I found out this weekend that the minimum idle adjustment I did a few weeks back appears to have been something other than the real minimum. The idle has been wandering lately, and didn't respond to my changing it to 1000rpm in the "Idle Speed VS Temp" table, so I started to bump it down to see if it would respond at all. It did, and the rpm finally bottomed at about 500. The minimum idle I had previously "set" was 700rpm at the TB, with 750rpm in the table above. Something's amiss. Parts: The IAC I'm using is from a ~2000 Dodge Ram truck, and appears to be *nearly* identical to the o-ring type of GM IAC with the 1x4-pin connector. Of course the pinout is different because Chrysler couldn't stand to use someone else's readily-available off-the-shelf part. I found the info I needed on the pinout on the Megasquirt Megamanual IAC Page, so I think I'm OK on the pure function side, it's now a question of "how much" so I can be sure the pintle is bottomed out. FWIW, the throttle body is the Mopar Performance billet 4V unit that uses all-Mopar sensors (TPS, IAC, MAP). The car runs and drives, but not very well, and I can't feel confident about tuning the lower end of the VE table until I get the basics tied down tight. Thanks in advance, after reading up for a couple years, I know y'all will come through for me! Clair

After reading a bit more, I'll refine part of my question. Since the ECM tells the IAC what to do, can I tell the IAC to do something while the engine is off with the IAC out, or do I have to have the engine running with the IAC ports blocked off?

Also, when talking counts, is zero the fully seated (no flow) position, or the fully open position? My understanding is that the Chrysler IAC has a finer movement than the GM o-ring IAC, so I will (possibly) need more counts to achieve the movement I want, but the ECM seems to control the idle to a degree now.

Thanks again,
Clair

zero is fully seated, to the best of my knowledge.

Looking at my datalogs, IAC throttle following functions will increase IAC counts with TPS and airflow
WOT-200 counts, 100% open.

You can pull the IAC out of the TB and leave it wired up. When you turn the key on you can watch the IAC move.
If you have a laptop or scanner hooked up you can see if it's moveing the right way. (High steps it will move in, Low steps it will move out)

So, it looks like I need to reduce my minimum idle speed at the TB again so I can see just how many counts are needed for the ECM to stop reducing idle speed. I wish I had the forethought to have looked at that when I was tinkering last weekend, but by that time I was pretty ticked off and it was almost bedtime for the monkey boy who was "helping" me.

In TPRT, my "IAC Park Position" constant is 180, which is increased from 160 previously (IIRC) with the ASSumption that zero was fully retrracted and the higher number would be more likely to seat the pintle on the orifice and close off flow. I've got some thinking to do...

Thanks for the replies, guys.

Clair

If you wish to seat the pintle closed against the orfice (no air flow):

Short A & B together on the ALDL connector
Key-on, engine-off
Wait 20 seconds, then disconnect the IAC connector (should be able to hear IAC clicking)
Key-off
Remove jumper from A & B

Pintle is seated.

Doing this with the IAC out of the throttle body will shoot the pintle across the garage.

RBob.

That's what I did when I initially set my minimum idle, but it was obvious that there was still some small amount of air bypassing the pintle. Maybe that's not a big deal, though. I guess I also need to verify the difference in the pintle-fully-seated length, and the "ejection point", too.

Just so I'm sure, will the A-B jumper operation extend the pintle until it bottoms, regardless of the settings in the bin?

Clair

Yes, it will continue to step closed until the connector is pulled, or the key is turned off. Once fully closed it will sit there and click. This is because it can not extend any further.

RBob.

OK, I think I'm getting this finally. Since there's no way for the ECM to know where the IAC sits (no feedback), it must just compare the existing idle speed to the target idle, and move the IAC accordingly. I guess I could seat the pintle, screw it back in fully counting the turns, and then calculate how many steps my particular unit needs for full range.

I guess it's not that big a deal if I'm not concerned with getting any more air through the TB at WOT and just controlling cold idle. Hmmm...

Clair

That is correct. The ECM sets the IAC fully closed in diagnostics mode as a reference point. It adjusts it from there.

You want the IAC full open at WOT? I think it was RBob that posted the calcs & tables on how do get it full open at WOT. He has posted a lot of IAC control stuff for decel, cruise, WOT. I can't remember where the thread is. It might be in the stickies.

ASSuming again on my part, but I guess the ECM bases it's fully-closed position on some minimal period of time that it takes to fully extend the IAC. That point (after being in the diagnostic for 5 seconds or whatever) becomes the new zero, and counts increase from there. That's easy enough to work with.

I'm NOT wanting the IAC wide open at WOT, or perhaps I should say that I don't care if it is. My TB is on the large side - 1000cfm, and it also has direct linkage on the throttle blades. All four barrels open at the same time and rate, so it's going to give me some "special" tuning problems all by itself. My engine is pretty mild, all things considered, so I'm not really concerned with getting 1050cfm out of the thing... I read a thread that discussed getting better throttle response by closing the IAC down as the throttle was opened, and that's more along my thinking at this point. With my minimum idle set pretty high (700rpm), I think my chances of stalling on rapid throttle close would be diminished. I think.

I need to go dig up more of RBobs IAC threads, though, I haven't seen those yet.

Clair