1994 k1500 IAC issue

[Marcus W]

Another IAC thread to add to the hundreds but I swear this one will be different! I can’t find any information on what I’m experiencing, (1994 k1500 5.7, tbi chips chip, newer remaned acdelco computer)my IAC moves and reacts to when I open the throttle blades, I can see it moving in the little port when I look down through the top of the throttle body with the truck running at temp, but when trying to do an idle relearn:
Cleared possible codes by disconnecting battery for 30 secs(SEL not giving me any just cleared to remove variables)
Truck at operating temp
Key on Jump A and B for 30 secs
Key off remove jumper
Start truck
IAC did not close, cannot see pintle In throttle body and idles at 1400 due to vacuum leak.
So I tested voltages at the pigtail with the key on, 0.47 on the 2 low sides and 11.6 on the two high sides
Haven’t tested my tps sensor since last year(when problem was noticed but I know it was In specs then, 0.5 at closed and 4.5 at wide open. Two almost brand new IAC are producing the same results which I guess it’s possible for them to be bad but I’m hesitant to buy another one at this time to try it.

 

[thinger2]

Another IAC thread to add to the hundreds but I swear this one will be different! I can’t find any information on what I’m experiencing, (1994 k1500 5.7, tbi chips chip, newer remaned acdelco computer)my IAC moves and reacts to when I open the throttle blades, I can see it moving in the little port when I look down through the top of the throttle body with the truck running at temp, but when trying to do an idle relearn:
Cleared possible codes by disconnecting battery for 30 secs(SEL not giving me any just cleared to remove variables)
Truck at operating temp
Key on Jump A and B for 30 secs
Key off remove jumper
Start truck
IAC did not close, cannot see pintle In throttle body and idles at 1400 due to vacuum leak.
So I tested voltages at the pigtail with the key on, 0.47 on the 2 low sides and 11.6 on the two high sides
Haven’t tested my tps sensor since last year(when problem was noticed but I know it was In specs then, 0.5 at closed and 4.5 at wide open. Two almost brand new IAC are producing the same results which I guess it’s possible for them to be bad but I’m hesitant to buy another one at this time to try it.

Its been awile but I pretty much did the same thing. Throttle body rebuild, new IAC, new TPS etc...
It was like I was asking the ecm to do too many things at the same time.
I reset base idle to 0 degrees with the dist. wire unplugged while the engine was hot.
I dont know how that procedure might change with a chip in it.
There is a spec for IAC pintle protrusion.
The pintle needs to be set at a particullar dimension before you power it.
I cant remember what that dimension is.
You can move that pintle in or out but you have to be very, very carefull.
The pintle shaft is attached to a very high reduction gear driven motor and it will break or strip the plastic gears easilly.
To move it in, put your thumb on the pintle and slowly push it in while drinking a beer.
Slow but firm.
To pul it out, do the same thing while pulling on the pintle.
Do not break the pintle stem.
And keep checking that dimension.
The other problem that was an absolute decoy was the IAC pigtail.
The contacts all tested just fine but I would loose IAC function when I plugged it back in.
That ended up being the crumbling internal plastic standoff pin guides.
When I pulled the plug it disconnected the short.
And tested good
When it put the plug back on It shorted again.
When you try to look up the IAC pigtail for your truck Orillys and Autozone and NAPA will claim that the pigtail they show "Will Not" fit your truck.
It does fit your truck. Ive had one on mine for at least 5 years.
It just isnt color coded. It comes with 4 black wires so you need to pay close attention to which wire goes where.
And, obviously, disconnect the battery first.
But it is a one way only plug and was 12 bucks and in stock.
Hope that helps

 

[Marcus W]

Its been awile but I pretty much did the same thing. Throttle body rebuild, new IAC, new TPS etc...
It was like I was asking the ecm to do too many things at the same time.
I reset base idle to 0 degrees with the dist. wire unplugged while the engine was hot.
I dont know how that procedure might change with a chip in it.
There is a spec for IAC pintle protrusion.
The pintle needs to be set at a particullar dimension before you power it.
I cant remember what that dimension is.
You can move that pintle in or out but you have to be very, very carefull.
The pintle shaft is attached to a very high reduction gear driven motor and it will break or strip the plastic gears easilly.
To move it in, put your thumb on the pintle and slowly push it in while drinking a beer.
Slow but firm.
To pul it out, do the same thing while pulling on the pintle.
Do not break the pintle stem.
And keep checking that dimension.
The other problem that was an absolute decoy was the IAC pigtail.
The contacts all tested just fine but I would loose IAC function when I plugged it back in.
That ended up being the crumbling internal plastic standoff pin guides.
When I pulled the plug it disconnected the short.
And tested good
When it put the plug back on It shorted again.
When you try to look up the IAC pigtail for your truck Orillys and Autozone and NAPA will claim that the pigtail they show "Will Not" fit your truck.
It does fit your truck. Ive had one on mine for at least 5 years.
It just isnt color coded. It comes with 4 black wires so you need to pay close attention to which wire goes where.
And, obviously, disconnect the battery first.
But it is a one way only plug and was 12 bucks and in stock.
Hope that helps

Replacing the pigtail is probably a good idea, I went ahead and ordered one aswell and a new iac just to start fresh with it, I do know how far the pintle stick out should be during install but I do know that it can’t be more than 29mm or it will bottom out but I can’t find anything on a specific length it needs to be.

 

[thinger2]

Replacing the pigtail is probably a good idea, I went ahead and ordered one aswell and a new iac just to start fresh with it, I do know how far the pintle stick out should be during install but I do know that it can’t be more than 29mm or it will bottom out but I can’t find anything on a specific length it needs to be.

I seems to me that it was a maximum protrusion of about .230 or so.
So less than 1/4 of an inch.
Dont take that for the truth though.
Im sure that 29mm is a typo on your part.
The reason it cant be to far out is that the end of the pintle will bottom in the seat before the IAC is threaded all of the way in.
When you tighten the IAC into place with the pintle extended to far, you are torqueing the gearset onto the pintle instead of pushing the pintle back into the gearset.
So the tapered end of the pintle binds on the seat inside the throttle body and stops turning.
All of that torque then goes to the pintle stem and then into the plastic gears.
And something breaks
In other words the pintle has to be retracted far enough to allow the case of the IAC to be tightened in place before the pintle touches the seat.
They are designed to move in and out only.
They will break with the slightest side load on that stem or gears.
Im digging around for that spec and for the old IAC I cut apart.
Its somewhere under all these friggen Nissan parts

 

[thinger2]

Replacing the pigtail is probably a good idea, I went ahead and ordered one aswell and a new iac just to start fresh with it, I do know how far the pintle stick out should be during install but I do know that it can’t be more than 29mm or it will bottom out but I can’t find anything on a specific length it needs to be.

I seems to me that it was a maximum protrusion of about .230 or so.
So less than 1/4 of an inch.
Dont take that for the truth though.
Im sure that 29mm is a typo on your part.
The reason it cant be to far out is that the end of the pintle will bottom in the seat before the IAC is threaded all of the way in.
When you tighten the IAC into place with the pintle extended to far, you are torqueing the gearset onto the pintle instead of pushing the pintle back into the gearset.
So the tapered end of the pintle binds on the seat inside the throttle body and stops turning.
All of that torque then goes to the pintle stem and then into the plastic gears.
And something breaks
In other words the pintle has to be retracted far enough to allow the case of the IAC to be tightened in place before the pintle touches the seat.
They are designed to move in and out only.
They will break with the slightest side load on that stem or gears.
Im digging around for that spec and for the old IAC I cut apart.
Its somewhere under all these friggen Nissan parts

 

[PlayingWithTBI]

Truck at operating temp
Key on Jump A and B for 30 secs
Key off remove jumper
Start truck
IAC did not close, cannot see pintle In throttle body and idles at 1400 due to vacuum leak.

I think you're skipping one important step.
Jump A & B, turn on key, engine off. Then disconnect the IAC connector with key still on, shut off engine and pull A/B jumper, start engine, and set min idle. This .pdf also shows how to set your TPS, it's old but works on our TBI trucks too.

 

[Marcus W]

I think you're skipping one important step.
Jump A & B, turn on key, engine off. Then disconnect the IAC connector with key still on, shut off engine and pull A/B jumper, start engine, and set min idle. This .pdf also shows how to set your TPS, it's old but works on our TBI trucks too.

I forgot to add the part about disconnecting the iac in my original post lol, a just gave that pdf a quick glance looks like it’s got lots of good info I’ll have the new pigtail by the end of next week and I’ll be able to give it a try and hopefully I get somewhere with it.

 

[Marcus W]

Its been awile but I pretty much did the same thing. Throttle body rebuild, new IAC, new TPS etc...
It was like I was asking the ecm to do too many things at the same time.
I reset base idle to 0 degrees with the dist. wire unplugged while the engine was hot.
I dont know how that procedure might change with a chip in it.
There is a spec for IAC pintle protrusion.
The pintle needs to be set at a particullar dimension before you power it.
I cant remember what that dimension is.
You can move that pintle in or out but you have to be very, very carefull.
The pintle shaft is attached to a very high reduction gear driven motor and it will break or strip the plastic gears easilly.
To move it in, put your thumb on the pintle and slowly push it in while drinking a beer.
Slow but firm.
To pul it out, do the same thing while pulling on the pintle.
Do not break the pintle stem.
And keep checking that dimension.
The other problem that was an absolute decoy was the IAC pigtail.
The contacts all tested just fine but I would loose IAC function when I plugged it back in.
That ended up being the crumbling internal plastic standoff pin guides.
When I pulled the plug it disconnected the short.
And tested good
When it put the plug back on It shorted again.
When you try to look up the IAC pigtail for your truck Orillys and Autozone and NAPA will claim that the pigtail they show "Will Not" fit your truck.
It does fit your truck. Ive had one on mine for at least 5 years.
It just isnt color coded. It comes with 4 black wires so you need to pay close attention to which wire goes where.
And, obviously, disconnect the battery first.
But it is a one way only plug and was 12 bucks and in stock.
Hope that helps

Got my new pigtail and iac in the mail today and went ahead and installed them, didn’t quite have the effect I was hoping for. When I started the truck up to get it to temp it did start and idle differently than before, a step in the right direction. So I went through the pdf you sent and set the base idle according to instruction but the iac still will not close when the an and b terminals are jumped. What I ended up doing is starting the truck like normal and seeing the pintle closed all the way I would unplug it and then set the idle like that, after that the truck didn’t want to start had to give it a little throttle went for a drive and there’s a major differnce in the way the truck performs in the low end. It’s much better now but it still bugs me that it won’t extend when the an and b ports are jumped, currently truck starts and drives great. After the test drive it fires up fine so I think I’m going to drive it a bit and then try setting it properly.

 

[thinger2]

Got my new pigtail and iac in the mail today and went ahead and installed them, didn’t quite have the effect I was hoping for. When I started the truck up to get it to temp it did start and idle differently than before, a step in the right direction. So I went through the pdf you sent and set the base idle according to instruction but the iac still will not close when the an and b terminals are jumped. What I ended up doing is starting the truck like normal and seeing the pintle closed all the way I would unplug it and then set the idle like that, after that the truck didn’t want to start had to give it a little throttle went for a drive and there’s a major differnce in the way the truck performs in the low end. It’s much better now but it still bugs me that it won’t extend when the an and b ports are jumped, currently truck starts and drives great. After the test drive it fires up fine so I think I’m going to drive it a bit and then try setting it properly.

I went through a bunch of problems when I replaced mine too.
But that was the same day I rebuilt the throttle body and put a new IAC and pigtail and a new TPS and temp sensor.
And a lot of new grounds.
That was the same day I put the new distributor in as well.
I bought the NOS part inventory from a shop that was going out of business and replaced all of my old parts with new all at the same time.
This is when some of the more experianced guys on this forumn will tell you that you need a scanner.
And you should get one if you are going to keep the truck.
But that doesnt help you right this minute.
Sometimes I think that if you were air dropped into Mexico and you went on this forumn asking about how to find the bathroom, some of these guys would tell you to just shut up and learn spanish.
I fought with mine all day.
Most of the procedures would not work correctly and every time I got one thing to work something else stopped working.
It was the battery cables.
Bad ground and low voltage to the ECM during relearn/reset.
If you have never replaced your battery cables they are bad.
They look brand new from the outside.
But wire rots inside of the plastic side post connections.
At the end of that wire and inside of that sidepost connection is a ring terminal on the end of the wire.
The wire corrodes and that ring terminal rots but the only damn miracle bulletproof plastic GM ever made is that coating on the ends of the battery cables.
When you tighten down an old GM side post connection the plastic reaches torque BEFORE the ring terminal has good contact.
It is binding on the plastic. Not on the ring end of the wire.
The plastic tightens up before the wire makes a solid contact.
Many many many people will tell you to go buy brand new GM battery cables.
But they might not work with an aftermarket battery.
And who has a genuine GM battery these days?
GM sidepost batteries have a plastic coller around the contact.
A type of a "standoff" connection.
That "Standoff" varies in my experiance about plus or minus about 0.125 or so
The only way you get any somewhat decent connection on an aftermarket battery is if that coller is 1/8ths short.
If its 1/8ths long you get nothing.
Take a pair of dikes or sidecutters and cut all of the plastic off of both ends of your battery cables without cutting the wire or the ring terminal.
They will be rotted.
I have never seen an old one that wasnt.
I can get you down the road for about 4 bucks of bolts nuts and washers without buying new battery cables.
Let me know, its really easy and Im on about year 5 or so of this rig.
The ecm relies on finding certain steady voltages from the various sensors.
Bad ground, low volts, high volts, intermittant, etc..
It doesnt meet the parameters and it wont reset.
And that all changes when the wires get hot.
Pretty much any strange bizarre thing that happens on any side post Chevy will turn into a friggen tail chase if you dont fix the sideposts first.
That might not cure your problem, but at least you will know that it isnt the problem.

 

[Marcus W]

I went through a bunch of problems when I replaced mine too.
But that was the same day I rebuilt the throttle body and put a new IAC and pigtail and a new TPS and temp sensor.
And a lot of new grounds.
That was the same day I put the new distributor in as well.
I bought the NOS part inventory from a shop that was going out of business and replaced all of my old parts with new all at the same time.
This is when some of the more experianced guys on this forumn will tell you that you need a scanner.
And you should get one if you are going to keep the truck.
But that doesnt help you right this minute.
Sometimes I think that if you were air dropped into Mexico and you went on this forumn asking about how to find the bathroom, some of these guys would tell you to just shut up and learn spanish.
I fought with mine all day.
Most of the procedures would not work correctly and every time I got one thing to work something else stopped working.
It was the battery cables.
Bad ground and low voltage to the ECM during relearn/reset.
If you have never replaced your battery cables they are bad.
They look brand new from the outside.
But wire rots inside of the plastic side post connections.
At the end of that wire and inside of that sidepost connection is a ring terminal on the end of the wire.
The wire corrodes and that ring terminal rots but the only damn miracle bulletproof plastic GM ever made is that coating on the ends of the battery cables.
When you tighten down an old GM side post connection the plastic reaches torque BEFORE the ring terminal has good contact.
It is binding on the plastic. Not on the ring end of the wire.
The plastic tightens up before the wire makes a solid contact.
Many many many people will tell you to go buy brand new GM battery cables.
But they might not work with an aftermarket battery.
And who has a genuine GM battery these days?
GM sidepost batteries have a plastic coller around the contact.
A type of a "standoff" connection.
That "Standoff" varies in my experiance about plus or minus about 0.125 or so
The only way you get any somewhat decent connection on an aftermarket battery is if that coller is 1/8ths short.
If its 1/8ths long you get nothing.
Take a pair of dikes or sidecutters and cut all of the plastic off of both ends of your battery cables without cutting the wire or the ring terminal.
They will be rotted.
I have never seen an old one that wasnt.
I can get you down the road for about 4 bucks of bolts nuts and washers without buying new battery cables.
Let me know, its really easy and Im on about year 5 or so of this rig.
The ecm relies on finding certain steady voltages from the various sensors.
Bad ground, low volts, high volts, intermittant, etc..
It doesnt meet the parameters and it wont reset.
And that all changes when the wires get hot.
Pretty much any strange bizarre thing that happens on any side post Chevy will turn into a friggen tail chase if you dont fix the sideposts first.
That might not cure your problem, but at least you will know that it isnt the problem.

I’m defiantly going to take a close look at my battery cables I’ve never thought of that before, I am interested in getting a scanner to make life easier do you have any recommendations?