Ronny

iTrader: (1)

I posted my difficulty in wiring my IAC correctly under TBI thread.

This morning it appears I have witnessed the IAC motor is functional as the cold high idle is apparent but idle increases as the coolant temp rises. Polarity needs to be reversed?

I think WU reported about 40 steps on cold cold start. I believe it is idle speed is commanded by RPM and that 40 steps seems about right for 1250 rpms.

At 190 F coolant temp the WU shows 5 steps which is as commanded in min idle steps, park-neu is commanded to 800 rpms and drive 800 rpms. a manual trans i have. Since car is idleing at 1800-2000 rpms it seems the WU reports what is in bin and not what is reality? Is this to be expected?

vernw

iTrader: (2)

Actually, the ECM reports what it TOLD the IAC to go to in terms of the number of steps. There is no feedback loop on the IAC to report what it went to steps-wise. I've actually had an IAC that froze up and wouldn't move, but the ECM didn't know that due to the lack of feedback. The datalogs still showed the IAC to be moving because they report what it is supposed to be sitting at.

Ronny

iTrader: (1)

that seems consistent.

thank you.

i will search and post how i have it currently wired. car is at home and i cant recall. i know who posted the wire scheme. all three posts with recommendations are different and do not work for me. the last one i used did get it moving but appears reversed polarity.

if tou have a chance check my post in TBI.

vernw

iTrader: (2)

I'm no TBI guru, but that's the way things work on the TPI set ups and the valves aren't that different (nor is the harness) between the two.

91chevz71

interesting. (the no feedback loop)

cool

VL21P-7730

Sounds like what mine was doing when I had the polarity to the coils reversed, although I didn't really have the high initial idle speed. Had to feather it at first, and then it was fine, but increased as it warmed up. I rewired per the instructions on the MS IAC page:
http://www.megamanual.com/ms2/IAC.htm

Since this is sort of keyed to what I was asking in my thread, I'll go refine my question a tad rather than ask here.

Clair

Ronny

iTrader: (1)

i reversed one of the two(A-B) last night on a warm engine. still high idle. will do the second (C-D) tonight?

i ran the voltage in the harness on a warm engine and got the voltage readings. What if I run the voltage readings on a cold engine? would they not be different? This would rule out ECU issue. Someone said it could be a ECU issue with drivers? I hope that is not the problem as I believe it is simply miswired.

I think I found like 5 different opinions on color code harness to IAC unit on this and CF site. so apparently there is a varied opinion? I think GM should be consistent on harness. right?

Does anyone agree that the green wires run one stepper motor and the blues run another? if so that cuts the options on wiring.

RBob

iTrader: (1)

That is the way I've always recall them being wired. The two greens run one coil, the two blues run the other coil.

If the IAC runs in reverse only need to reverse one pair of wires.

RBob.

Ronny

iTrader: (1)

Thanks. that makes it easier. i will restore one and flip the other tonight.

Dominic Sorresso

Ron,

Has this always happened? Could it be the wiring if it hasn't?? I've had a problem intermittently with the IAC not idling down when I would first put a new bin in the Ostrich and then start the car. After the first start-up, it would act fine.

Ronny

iTrader: (1)

Hi Dom: the IAC was never functional as far as cold start. cold start enrichment was there and car idled at 775 rpms on warm up in driveway. car did not die so no issue. as far as throttle follwer and that i will say never moved yet i have no way of determining. WU showed the commands to IAC which I believe to be dead. warm engine car idled 875 rpms which i lived with.

now i flipped one of the two sets of leads(blue or green) yesterday and on cold start it went to 1250 and i thought all was well. on warm engine rpms dropped to 775-800(as commanded) which it never did before. apparently the pindle was never seated so always had 875 for warm idle. so i thought this is great.

now this i cant explain. cold start this morning car idled at 2200 and never dropped even though coolant rose to 200F. so it appears now it is fully retracted?

I looked up the schmatic for the 1984 crossfire so will use stock harness configuration to my 7.4LTBI and start over. do you think GM kept ABCD the same ? they are both flat connectors.