87 Chevy TBI IAC Troubleshooting

[87ChevyV20]

I am working on Ole Blister and I am having idle problems.

It was having trouble when you first start it and the idle was too low and it would die.
Keeping the RPM's up to 1000 for a few minutes would solve it until it was warm.
Still didn't run perfect, but it ran.

I have had to replace the distributor and time it a few months ago, that is good.
I have been fixing vacuum leaks, basically I have run all new hoses, so that should be good.

It was still running the same so I decided to clean the IAC valve, then decided to clean the throttle body.
I got an AC Delco gasket kit for the throttle body (First one was missing the fuel pressure regulator gasket) and cleaned the IAC.
I used this video to clean the IAC. It didn't seem that bad, but cleaned it up perfect.
I used this video as a reference for the TBI rebuild, minus the injectors because my injectors seem to be spraying fine.

I have been using my Moates ALDL cable and TunerPro to monitor the engine vitals.
The IAC counts are moving around like they should and one of my questions is are the IAC counts in TunerPro the actual position of the IAC or is that what the ECM is commanding the IAC to do?
I ask this question because it doesn't seem like my IAC valve is moving.

Once I started the engine after cleaning the IAC and TBI, it started right up faster than before and idled at about 2500 RPM.
Seems logical after having the IAC retracted fully for reinstallation.

After I warmed the engine up, I did the idle relearn procedure and I thought that would put the tip of the IAC valve into the IAC passage in the TBI.
I don't think the IAC is actually moving though.
I took out the IAC and it was in the same position as it was when I installed it.

I figured the IAC was bad as it wasn't moving, so I ran and bought a new one.
I don't think that is moving either so it must be an issue with the wiring?

So again, my questions are
Do the IAC counts in TunerPro show the actual position of the IAC or is that what the ECM is commanding the IAC to do?
After doing the idle relearn procedure, shouldn't I see the tip of the IAC valve sticking through the IAC passage from the top of the TBI?
Does anyone have a testing procedure for the wiring of the IAC?

There are no codes so I am at a loss.

Thanks for the help, as always!

 

[87ChevyV20]

Oh, and I replaced the EGR valve while I had the throttle body off as that was as good a time as any.

The EGR did hold a vacuum but not very long so it needed replacement.

 

[gmbellew]

IAC counts are the position the ECM thinks the IAC is in. you can relearn it by jumpering AB on the ALDL and key on for 30-45 sec to fully close IAC. then key off and pull the jumper. then start it up and see how IAC counts change. idle should be high on a cold start and IAC counts should slowly drop as the ECM idles it down.

 

[87ChevyV20]

I've tried that, and I think the new IAC is clicking as I didn't have that before with the old IAC.

Maybe I will retry that and leave the ALDL pins jumped for longer.
I only did it for 10 or so seconds before.

 

[87ChevyV20]

According to the wiring diagram, all 4 wires go to the ECM.

I guess I can check them for continuity.

You must be registered for see images attach

 

[87ChevyV20]

I left the ALDL pins jumped for at least 10 minutes with no change in the idle speed.

I should be able to see the tip of the IAC valve through the top of the throttle body?

 

[Mango]

Did you clear the EMC?

 

[87ChevyV20]

How would I do that?

 

[1STLS1]

Checking the continuity to the ECM is a good idea, I think they have replacement pig tails on Rock auto for that. I found on 2 of my trucks the EGR solenoid causing a vacuum leak. I blocked off it's vacuum source to verify.

 

[87ChevyV20]

Did you clear the EMC?

Oh, I have done that when I installed the TBI and new EGR valve, but before the new IAC.

 

[gmbellew]

I left the ALDL pins jumped for at least 10 minutes with no change in the idle speed.

I should be able to see the tip of the IAC valve through the top of the throttle body?

you jumper AB, turn ignition to ON but do not start, leave it for 30sec, turn ignition to OFF, remove jumper. then start the truck and see what IAC and the idle do. I think having AB jumpered when you start is some sort of diagnostic mode or something. I dont recall off the top of my head.

 

[87ChevyV20]

Yeah, I did that.

 

[87ChevyV20]

Researching a bit and found this guys video explaining the technicals of the idle air control.

So I ran outside real quick and tested the 4 wires at the IAC and they all had some sort of activity.
That should mean the wiring to the IAC is good?

I am leaning towards a bad IAC valve, even though it is new?

 

[gmbellew]

so when you started it up, the idle doesn't start higher and idle down as the engine warms? what is the idle speed?

you can jumper AB and force the IAC to close as i described above. then if you unplug the IAC and start the truck, the idle should be lower than normal idle. bc the IAC is all the way closed. if the idle is still very high like that, either somebody messed with the idle set screw (behind a knock out plug) or you have a large vacuum leak somewhere.

 

[Strick]

Just did an ECM replacement on my '87. It ran super FAT at idle (iraddic) & would not remit any trouble codes. Swapped with another ECM & it strained the issue out.

HS