resetting the iac - The 1947 - Present Chevrolet & GMC Truck Message Board Network

.38 special · 12-17-2003, 01:24 AM

I know I have asked before, but I can't remember and couldn't find the thread. But how do you reset the IAC valve again on the TBI350? It idles really low now because I reset it before while I had a leak in the TB gasket. I didn't mind the low idle, but it dies every once in a while when I stop real fast and I am worried that it is gonna stall in an intersection.
Thanks

**swervin ervin** · 12-17-2003, 12:00 PM

Leave the IAC connected and put a jumper in terminal A and B (two top row terminals on the far right). Turn the ignition switch on, but do not start the engine. Wait at least 30 seconds to give the IAC time to fully seat. With the ignition switch still on, disconnect the IAC. Remove the jumper wire from the diagnostic connector and start the engine. Let the engine reach normal operating temp. Set the park brake and with the engine in drive, adjust the idle stop screw to 500-550 rpm for an auto, and 600-650 rpm for a manual. Turn the engine off and reconnect the IAC.

That's it.

TwinTurbo · 12-17-2003, 01:28 PM

The IAC motor will cycle with the ALDL connector jumpered, you need to pull the jumper when it's seated

**swervin ervin** · 12-17-2003, 01:42 PM

Sorry, my post was to set the minimum idle speed. This also resets the IAC, but it also makes sure you have the minimum speed set so you won't have problems like you describe.

TwinTurbo · 12-17-2003, 01:45 PM

The IAC's will reset themselves automatically if you go over 35 mph, you don't have to do anything to them at all

Marck

.38 special · 12-17-2003, 11:18 PM

Marck,
Do you mean after you jump the aldl? Or all of the time it is self-adjusting? If that is true, then why is the idle so low? What else could it be.

Swervin Ervin,
There is only one problem: I don't have an idle stop screw. Where the screw normally is, is a little stub, that is molded onto the throttle body itself.

I did however, jump the aldl and let it seat. Then let it run and plugged it back in. And that did help just a little (I think). But so little that it is hard to tell a difference.

Still got a problem here and any help would be appreciated.

Also while I am at it, where should the TBS be set at?

**swervin ervin** · 12-17-2003, 11:43 PM

Joe,

oh but yes you do have a idle stop screw. It's just covered up with a plug. Remove the plug and you will see it. They have it covered because they didn't want everyone thinking you could adjust the idle speed, which you can't. The computer controls the idle speed. All this screw does is set the minimum speed.

.38 special · 12-18-2003, 12:50 AM

where, what plug? I really didn't see one. is it rubber?

**swervin ervin** · 12-18-2003, 01:55 AM

There is a metal cap/plug sort of thing that fits in the hole where the idle stop screw is located. You will need to use something sharp like a scratch awl or similar to punch a hole in it and pry it out. It's not that hard to get out.

.38 special · 12-19-2003, 01:53 AM

ok.
I know exactly what you are talking about. They sure hid it well, because that really looks like just part of the throttle body. It is good to know that nobody has ever messed with it.

I guess when I bought the truck (several months ago) the guy wasn't lying. He told me the valve covers had never even been off. It has 199,000 miles on it and still runs like a new truck (other than this stupid little problem). You gotta love GM.

**swervin ervin** · 12-19-2003, 02:15 AM

Most of the time, you would never touch it. But when you start replacing parts on the TBI, you have to I guess. It for sure won't hurt anything to make sure it's set to the right minimum rpm. Just don't think you can use it to raise the idle rpm. It ain't going to happen. Once the computer is hooked back up to it, it takes over everything.

Reason I messed with mine, on the 87 van I'm selling, is because I had a high idle. No matter what I did, I still had a high idle. I finally got a used throttle body and rebuilt it. Mine had some terribly worn throttle shafts. On the old one, someone had already tried to lower the rpm and had messed with the screw. I figured it was way off wack. Had nothing to do with a high idle rpm. But I do know you can set the minimum idle for sure.

Keep us informed if this fixes your problem.

.38 special · 12-19-2003, 02:32 AM

Thanks, and I will keep you posted. I won't get a chance to work on it until this weekend though.

.38 special · 12-21-2003, 01:53 PM

Worked like a charm. Thanks Ervin. It still isn't real consistant though, but much better. Also while I'm at it where should the TPS be set at.

Grim Reaper · 12-21-2003, 08:09 PM

Are you sure your not just covering up another problem by idleing it up?
There are several things that could cause these symtoms.
EGR being open at Idle could cause it.
Ports in the throttle body plugged up.
PCV problems.
All those could cause a idle issue.

.38 special · 12-23-2003, 08:52 PM

I don't think I am covering anything up. I had a high idle a little while back and tried to adjust the IAC then-but didn't work. Ended up being a leak in the TB gasket causing the high idle. After I fixxed it the idle was very low. I think because the IAC was pretty much shut because I adjusted it when there was a throttle body leak. I just dealt with the low idle for a little while, until I started this new job where I was driving alot and in alot of traffic. So I don't think I have another problem and it runs fine and hasen't thrown any codes. But you could be right--how can I check for these things to be sure?

12-17-2003, 01:24 AM	#1
.38 special Registered User Join Date: Oct 2003 Location: Houston area Posts: 65	resetting the iac I know I have asked before, but I can't remember and couldn't find the thread. But how do you reset the IAC valve again on the TBI350? It idles really low now because I reset it before while I had a leak in the TB gasket. I didn't mind the low idle, but it dies every once in a while when I stop real fast and I am worried that it is gonna stall in an intersection. Thanks __________________ Turbo Joe 1987 GMC sierra 1987 Buick Turbo Regal

12-17-2003, 12:00 PM	#2
swervin ervin You get what you pay for Join Date: Dec 1999 Location: Cherryville, NC Posts: 4,798	Leave the IAC connected and put a jumper in terminal A and B (two top row terminals on the far right). Turn the ignition switch on, but do not start the engine. Wait at least 30 seconds to give the IAC time to fully seat. With the ignition switch still on, disconnect the IAC. Remove the jumper wire from the diagnostic connector and start the engine. Let the engine reach normal operating temp. Set the park brake and with the engine in drive, adjust the idle stop screw to 500-550 rpm for an auto, and 600-650 rpm for a manual. Turn the engine off and reconnect the IAC. That's it. __________________ Mike 1985 Chevy C-10

12-17-2003, 11:18 PM	#6
.38 special Registered User Join Date: Oct 2003 Location: Houston area Posts: 65	Marck, Do you mean after you jump the aldl? Or all of the time it is self-adjusting? If that is true, then why is the idle so low? What else could it be. Swervin Ervin, There is only one problem: I don't have an idle stop screw. Where the screw normally is, is a little stub, that is molded onto the throttle body itself. I did however, jump the aldl and let it seat. Then let it run and plugged it back in. And that did help just a little (I think). But so little that it is hard to tell a difference. Still got a problem here and any help would be appreciated. Also while I am at it, where should the TBS be set at? __________________ Turbo Joe 1987 GMC sierra 1987 Buick Turbo Regal

12-18-2003, 12:50 AM	#8
.38 special Registered User Join Date: Oct 2003 Location: Houston area Posts: 65	where, what plug? I really didn't see one. is it rubber? __________________ Turbo Joe 1987 GMC sierra 1987 Buick Turbo Regal

12-19-2003, 01:53 AM	#10
.38 special Registered User Join Date: Oct 2003 Location: Houston area Posts: 65	ok. I know exactly what you are talking about. They sure hid it well, because that really looks like just part of the throttle body. It is good to know that nobody has ever messed with it. I guess when I bought the truck (several months ago) the guy wasn't lying. He told me the valve covers had never even been off. It has 199,000 miles on it and still runs like a new truck (other than this stupid little problem). You gotta love GM. __________________ Turbo Joe 1987 GMC sierra 1987 Buick Turbo Regal

12-17-2003, 01:28 PM	#3
TwinTurbo Registered User Join Date: Sep 2003 Location: The Netherlands Posts: 994	The IAC motor will cycle with the ALDL connector jumpered, you need to pull the jumper when it's seated

12-17-2003, 01:42 PM	#4
swervin ervin You get what you pay for Join Date: Dec 1999 Location: Cherryville, NC Posts: 4,798	Sorry, my post was to set the minimum idle speed. This also resets the IAC, but it also makes sure you have the minimum speed set so you won't have problems like you describe.

12-17-2003, 01:45 PM	#5
TwinTurbo Registered User Join Date: Sep 2003 Location: The Netherlands Posts: 994	The IAC's will reset themselves automatically if you go over 35 mph, you don't have to do anything to them at all Marck

12-17-2003, 11:43 PM	#7
swervin ervin You get what you pay for Join Date: Dec 1999 Location: Cherryville, NC Posts: 4,798	Joe, oh but yes you do have a idle stop screw. It's just covered up with a plug. Remove the plug and you will see it. They have it covered because they didn't want everyone thinking you could adjust the idle speed, which you can't. The computer controls the idle speed. All this screw does is set the minimum speed.

12-18-2003, 01:55 AM	#9
swervin ervin You get what you pay for Join Date: Dec 1999 Location: Cherryville, NC Posts: 4,798	There is a metal cap/plug sort of thing that fits in the hole where the idle stop screw is located. You will need to use something sharp like a scratch awl or similar to punch a hole in it and pry it out. It's not that hard to get out.

12-19-2003, 02:15 AM	#11
swervin ervin You get what you pay for Join Date: Dec 1999 Location: Cherryville, NC Posts: 4,798	Most of the time, you would never touch it. But when you start replacing parts on the TBI, you have to I guess. It for sure won't hurt anything to make sure it's set to the right minimum rpm. Just don't think you can use it to raise the idle rpm. It ain't going to happen. Once the computer is hooked back up to it, it takes over everything. Reason I messed with mine, on the 87 van I'm selling, is because I had a high idle. No matter what I did, I still had a high idle. I finally got a used throttle body and rebuilt it. Mine had some terribly worn throttle shafts. On the old one, someone had already tried to lower the rpm and had messed with the screw. I figured it was way off wack. Had nothing to do with a high idle rpm. But I do know you can set the minimum idle for sure. Keep us informed if this fixes your problem.

12-19-2003, 02:32 AM	#12
.38 special Registered User Join Date: Oct 2003 Location: Houston area Posts: 65	Thanks, and I will keep you posted. I won't get a chance to work on it until this weekend though. __________________ Turbo Joe 1987 GMC sierra 1987 Buick Turbo Regal

12-21-2003, 01:53 PM	#13
.38 special Registered User Join Date: Oct 2003 Location: Houston area Posts: 65	Worked like a charm. Thanks Ervin. It still isn't real consistant though, but much better. Also while I'm at it where should the TPS be set at. __________________ Turbo Joe 1987 GMC sierra 1987 Buick Turbo Regal

12-21-2003, 08:09 PM	#14
Grim Reaper Registered User Join Date: Jul 2001 Location: Atlanta GA Posts: 1,704	Are you sure your not just covering up another problem by idleing it up? There are several things that could cause these symtoms. EGR being open at Idle could cause it. Ports in the throttle body plugged up. PCV problems. All those could cause a idle issue. __________________ Grim-Reaper 70 Pontiac LeMans Sport Convertible, worlds longest resto in progress Looking for 71-72 2wd Blazer or Jimmy Project

12-23-2003, 08:52 PM	#15
.38 special Registered User Join Date: Oct 2003 Location: Houston area Posts: 65	I don't think I am covering anything up. I had a high idle a little while back and tried to adjust the IAC then-but didn't work. Ended up being a leak in the TB gasket causing the high idle. After I fixxed it the idle was very low. I think because the IAC was pretty much shut because I adjusted it when there was a throttle body leak. I just dealt with the low idle for a little while, until I started this new job where I was driving alot and in alot of traffic. So I don't think I have another problem and it runs fine and hasen't thrown any codes. But you could be right--how can I check for these things to be sure? __________________ Turbo Joe 1987 GMC sierra 1987 Buick Turbo Regal



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