IAC Problems

[redrockexplorer]

MY 93 explorer IAC does not work for 1min to 10min after starting engine. It seems longer it sits unstarted longer IAC takes to start working. Relaced couple IACs decided it was not the problem. Runs fine after IAC starts working. Replaced left O2 sensor, codes 176 and 177. Only code it has now is 629 and it has had this code the whole time i've owned it and the TC lock-up works fine. Read on here to check ECT and IAT sensors. The IAT metered ok, ECT metered open so I replaced it. MAF has been cleaned and TPS is at .94 volts. Still having same problem. Then I remembered my meter also measures duty cycles. so i back probed IAC connection. The IAC is not getting a signal from PCM until it works. I have cleaned the connections at PCM and the 2 beside the alt is there any connections i'm missing? Could a sensor hold out the PCM from sending signal? Or is my PCM bad?

 

[nitro71]

I'm not a whiz at these computers yet.. But I'd say the fact that it does get the signal says the computer is working fine. Whatever parameters need to be set before it "turns" it on are not happening for some reason. I'm supposing the engine is running poorly at idle until the PCM turns the IAC on?

 

[doonze]

The way I read it Nitro, there IS no signal, until it starts working.... In other words if I understand what he is saying, he test at the IAC...no signal..... time goes by... all of a sudden there's a signal and everything works from then on. Just takes X mins or so for the IAC to get a signal at all from the PCM.

Course I may be splitter hairs here, I think maybe what you were saying is that since the signal FINALLY gets there that the PCM is ok?

I'm going to play devils advocate here and jump on the other side of the fence. If you have tried several IAC's, then I would think it was the PCM.

I'm not 100% on any of this, MrShorty might have some insite on this, we'll see if he post up. But all in all I'd say your barking up the right tree at least. Wire short or PCM would be top of my list too.

Course there could always be ANOTHER sensor somewhere that tells the PCM it's time to start working the IAC.... I just don't know enough to say.

But I think from what I've read the IAC should ALWAYS have a signal of some sort. So reason would say, no signal = signal sender is bad? (PCM) If I'm thinking correctly.

 

[redrockexplorer]

The way I read it Nitro, there IS no signal, until it starts working.... In other words if I understand what he is saying, he test at the IAC...no signal..... time goes by... all of a sudden there's a signal and everything works from then on. Just takes X mins or so for the IAC to get a signal at all from the PCM..

doonze you are correct thats what it is doing. Its got me scratching my head.

 

[redrockexplorer]

Well I replaced the PCM with a reman unit from cardone and seem to fix my problem. Not even throwing a 629 code (TCC solenoid circuit failure ) since PCM was changed. Fuel mileage dosen't seem to be as good though.