My 86GT is idling high and eratic (1300 to 1700 RPM) in neutral or park. It runs rough at low RMPs (below 2000) and it seems to be OK when running over 2000 RPM. A friend read codes for me and indicated it needs the IAC cleaned or replaced. Can someone give me a step by step on how to remove it? Thanks.

on a V6
i take a box an inch and a quarter and take it out
unplug the harnees of the TPS just on top of it and the IAC harness too
Very easy job

Also might be an EGR problem. The EGR valve opens at light throttle so above 2000 rpm you don't notice any problem, but down low when the valve should be closed you get a crappy idle. Temporarily block off the EGR valve at the plenum and see if it gets better. Use a pop can or some slim piece of aluminum.

I just cleaned the IAC on my car...it was really simple. It just took a while to take it out but once it was it was really simple to clean it ... just make sure you clean it with throttle body cleaner NOT carberator cleaner. ahaha. once its clean and dry its ready to put back in just like that. Pretty awesome. Too bad my car blew up a week later. I doubt that will happen to you.

Alona Hudini and Thanks for the reply. Tell me more about the EGR, i.e. what does EGR stand for? where is it located? if I run the "block the EGR" test and it indicates it's part of the problem, do I clean it or replace it?

P.S. Yup, you are dealing with an absolute novice at this electronic and fuel injection stuff, but I am having a ball with it. I am an old school street rodder. The most advanced thing I have dealt with is an EFI distributor so I guess my expertise is absolete by about 25 years.

quote Originally posted by Hudini: Also might be an EGR problem. The EGR valve opens at light throttle so above 2000 rpm you don't notice any problem, but down low when the valve should be closed you get a crappy idle. Temporarily block off the EGR valve at the plenum and see if it gets better. Use a pop can or some slim piece of aluminum.

No problem. The EGR is Exhaust Gas Recirculation and is a mushroom shaped device located on the crossover pipe below and to the right of the throttle body. It's designed to reduce emissions by cooling the combustion temps when a small amount of exhaust is allowed back into the intake. The valve is only supposed to open though under light throttle. Idle and WOT it should be closed. If the valve itself goes bad, some exhaust gets back into the intake at idle and causes issues.

The test I refer to blocks the EGR tube that enters under the upper plenum, below and behind the throttle body. By placing something temporarily between the tube and intake you remove the EGR valve from the system. If the car runs better then you have your problem. If it runs the same, then gotta keep looking.

Looks like this:


This is the bottom of the plenum. The EGR tube is shown to the left of the pic. You can see how it connects:

quote Originally posted by formulachik: I just cleaned the IAC on my car...it was really simple. It just took a while to take it out but once it was it was really simple to clean it ... just make sure you clean it with throttle body cleaner NOT carberator cleaner. ahaha. once its clean and dry its ready to put back in just like that. Pretty awesome. Too bad my car blew up a week later. I doubt that will happen to you.

I had this idling problem for proably 10 years before finally fixing it. The car would idle OK during warm up and then vary (sometimes wildly) later. Especially when hot. All I did was spray throttle body cleaner in the TB opening while the car was idling. Especially in the tiny hole (I think) going to the IAC. I cleaned the whole darn thing and Viola! it idled like a champ! I am fairly positive it was the cleaning of the IAC that did it.

Thanks sjmaye!

Can I use carburator cleaner instead of throttle body cleaner? I live in a samll town in Hawaii. We have a small NAPA and a smaller CARQUEST. Neither store carries TB cleaner. Then there is WalMart and K-Mart but that means driving into town.

Did you probe the tiny whole going to the IAC or did you just spray it?

quote Originally posted by sjmaye: I had this idling problem for proably 10 years before finally fixing it. The car would idle OK during warm up and then vary (sometimes wildly) later. Especially when hot. All I did was spray throttle body cleaner in the TB opening while the car was idling. Especially in the tiny hole (I think) going to the IAC. I cleaned the whole darn thing and Viola! it idled like a champ! I am fairly positive it was the cleaning of the IAC that did it.

I'm also having an idle problem, after the car gets warmed up if I stop at a light the rpm will drop below 1k and keep falling till about 600/700 rpm in which the car almost dies and then fixes it self and goes back up to 1k rpm and continues this process indefinitely. I've taken out the IAC and it was filthy you couldn't even tell what color the spring was and everything was covered in this greasy soot stuff, I cleaned it all off and it made no difference. Any ideas?

quote Originally posted by KONADOK: Thanks sjmaye! Can I use carburator cleaner instead of throttle body cleaner? I live in a samll town in Hawaii. We have a small NAPA and a smaller CARQUEST. Neither store carries TB cleaner. Then there is WalMart and K-Mart but that means driving into town. Did you probe the tiny whole going to the IAC or did you just spray it?

To be honest I am not exactly sure it was throttle body cleaner. It probably was carb cleaner. I remember making sure it was safe for injectors. Although I do not see it in the photos posted above I distinctly remember sticking the red tube from the cleaner can in a tiny hole that I believe ran to the IAC. I sprayed it directly in this hole giving it a good cleaning. In fact, I am fairly sure it is the only part of the cleaning that affected the idle.

I just started the car and cleaned away! If I sprayed too much it would tend to bog down and try to die, so I backed off to keep it running.

No kidding this worked for me. I had this problem from when I bought the car in 1993 until probably 2005. Early on I had looked and replaced at a bunch of different sensors and such with no luck. I just gave up. Then one day I had the boot off between the air cleaner and the TB and saw how dirty it was. I decided to give it a good cleaning. The rest was history.

My only regret was that I was saddled with that crappy idle for a decade and the fix was so easy!

[This message has been edited by sjmaye (edited 08-24-2007).]

quote Originally posted by Hudini: Here is a pic of the throttle body. IAC is lower right: Take big wrench: Unscrew IAC:

Hudini, is that a aftermarket IAC valve you got there??

If its a Standard engine product "brand", has it worked well?? Just wondering if its just as good as AC Delco...

Thanks,

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fierogt28

88 GT, loaded, 5-speed

It actually came on the car when I bought it. Odds are its the lowest price one available in Sarasota, FL where I bought the car. Every part that had been replaced was the cheap stuff including the ignition module. About 3 hours and 180 miles into my ownership the car died. It turned out to be the cheap ignition module.

i don't believe anyone mentioned that the aic has an adjustment that must be met for it to work properly, check the manual for correct adjustment i thinks its under 1" 1/8

quote Originally posted by circlegear: i don't believe anyone mentioned that the aic has an adjustment that must be met for it to work properly, check the manual for correct adjustment i thinks its under 1" 1/8

It needs to be set at 1 1/8" before installing it or it may be damaged.

could also be vacuum leaks. I know i've been chasing them on my '86 duke like crazy.

quote Originally posted by circlegear: i don't believe anyone mentioned that the aic has an adjustment that must be met for it to work properly, check the manual for correct adjustment i thinks its under 1" 1/8

If I remember correctly, by jumpering the A+B terminals on the aldl connector (diagnostic mode) and key put in run (without starting) the iac should calibrate itself...you can actually hear it when it does.

for the record,
IAC= Idle Air Control (as opposed to "adjustment")
check that your vacuum hoses are ALL okay (especially the one the bottom of the throttle body)
clean the throttle body w/ carb/injector cleaner (spray can type)
change the IAC to a new one; before inserting depress the "plunger", screw in new unit, wire up; drive the car over 35 mph to reset the thing and the ECM

if that doesn't solve the problem, change the TPS (throttle position sensor), drive the car over 35 mph to reset the thing and the ECM

most L44 (V-6) idle problems are due to these two parts, aging not so gracefully, falsely communicating w/ the ECM

the good side of it is that they are cheap to replace

BTW, is the IAC valve from GM still available or AC Delco??

The GM or AC Delco part number would be handy to have for reference.

Not to hi-jack, but this would be good info to have so folks finding a OEM replacement would be a breeze. Just trying to make it easier for us.

TIA,

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fierogt28

88 GT, loaded, 5-speed

10031441 is the P/N. Rock Auto has Airtex and Standard which both have the brass look of Hudini's 'cheapo'.

Here's a dirty and a clean OEM unit.



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Notchbacks RULE

"Let a man drive a Fiero and he'll own one.
Teach a man to fix a Fiero and he'll own eight....errr...nine."

[This message has been edited by Fierobruiser (edited 12-22-2008).]

quote Originally posted by Fierobruiser: 10031441 is the P/N. Rock Auto has Airtex and Standard which both have the brass look of Hudini's 'cheapo'. Here's a dirty and a clean OEM unit.

I went on the AC Delco site and the P/N won't come up. Is this IAC valve used on other GM cars or pick-ups?? I sure it does, but from what engine?

BTW, thanks for the input...

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fierogt28

88 GT, loaded, 5-speed

I bought an IAC from my local NAPA. It looked pretty good. However, on this adjustment thing, I don't understand it. There are multiple comments on it: (1) you have to adjusted it or it will be damaged; (2) you have to manually connect two wires to have it adjust; or (3) it automatically adjusts after driving it. When I took out my old one, the plunger wouldn't move for anything. When I got the new one, the plunger would smoothly move, but with medium pressure. It seemed that as I screwed it in, it would seat itself, and certanly not damage anything. Does anyone actually have an answer that resolves these conflicting suggestions?

FWIW, my symptoms are that it idles fine when cold. But, after about 15 minutes of freeway driving, it won't hold idle. I have not changed the Throttle Position Sensor. Perhaps I'll look into that. Someone else was suggesting I "trick" it by adjusting the butterfly open a little at all times. I'd hate to do that, but will if I have to.

DO NOT tamper with the idle adjustment screw! If you have then you have wasted time of messing with the IAC. The whole purpose of the IAC is to control incoming air that is bypassing the butterfly to effectively control the idle. If you open the butterfly with the set screw ( which was actually capped from the factory ) your not allowing the IAC to perform it's function AND the TPS will read even more voltage which throws even more off.

Simply back out the throttle set screw until the butterflow just barely catches in the bore, and has a smooth open and close ( no catching ), clean THE HELL OUT OF the IAC and IAC passage, ensure that the TPS is reading .45mv at idle ( key on engine off - can be tweaked by manipulating the TPS throw arm with pliers ).

The IAC will self adjust in the bore once installed, simply jumper A and B together before plugging the 4 pin connector back on to the IAC ( MAKE SURE IAC IS INSTALLED INTO THROTTLEBODY BEFORE PLUGGING IN ). The 1 1/8" is the extent of the pintle travel inside the bore, however can travel further when it is removed. If the pintlle is further out than 1 1/8" when installed, you will simply crush the stepper motor and related parts inside the IAC casing.

So to sum it up..
1. Remove IAC, clean the PISS out of everything
2. Ensure set screw has not been tampered with, if it has, reset it as stated above
3. Make sure TPS reads .45mv at Key ON Engine OFF
4. adjust pintle length to 1 1/8" -measured from mounting surface of IAC casing to tip of pintle
5. Install
6. Jumper A and B in the ALDL to put into diagnostic mode
7. Plug 4 pin connector into IAC, you will hear the stepper motor bottoming out the pintle at the end of the bore inside the Throttlebody
8. Remove jumper
9. Start Car - there may be some initial hesitation, and even dying from the motor the first 2-3 starts, the IAC will self adjust
10. Check for vacuum leaks by covering the IAC inlet passage inside the bore of the TB with your finger, if the engine continues to run at ANY RPM, you do indeed have a vacuum leak

Class dismissed

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Recanizin' Flat-Buns Since 2001

Eric Nelson
Internet Sales Manager
Power Ford Valencia
nelsone@autonation.com

quote Originally posted by Chicken McNizzle: DO NOT tamper with the idle adjustment screw! If you have then you have wasted time of messing with the IAC. The whole purpose of the IAC is to control incoming air that is bypassing the butterfly to effectively control the idle. If you open the butterfly with the set screw ( which was actually capped from the factory ) your not allowing the IAC to perform it's function AND the TPS will read even more voltage which throws even more off. Simply back out the throttle set screw until the butterflow just barely catches in the bore, and has a smooth open and close ( no catching ), clean THE HELL OUT OF the IAC and IAC passage, ensure that the TPS is reading .45mv at idle ( key on engine off - can be tweaked by manipulating the TPS throw arm with pliers ). The IAC will self adjust in the bore once installed, simply jumper A and B together before plugging the 4 pin connector back on to the IAC ( MAKE SURE IAC IS INSTALLED INTO THROTTLEBODY BEFORE PLUGGING IN ). The 1 1/8" is the extent of the pintle travel inside the bore, however can travel further when it is removed. If the pintlle is further out than 1 1/8" when installed, you will simply crush the stepper motor and related parts inside the IAC casing. So to sum it up.. 1. Remove IAC, clean the PISS out of everything 2. Ensure set screw has not been tampered with, if it has, reset it as stated above 3. Make sure TPS reads .45mv at Key ON Engine OFF 4. adjust pintle length to 1 1/8" -measured from mounting surface of IAC casing to tip of pintle 5. Install 6. Jumper A and B in the ALDL to put into diagnostic mode 7. Plug 4 pin connector into IAC, you will hear the stepper motor bottoming out the pintle at the end of the bore inside the Throttlebody 8. Remove jumper 9. Start Car - there may be some initial hesitation, and even dying from the motor the first 2-3 starts, the IAC will self adjust 10. Check for vacuum leaks by covering the IAC inlet passage inside the bore of the TB with your finger, if the engine continues to run at ANY RPM, you do indeed have a vacuum leak Class dismissed

That's good info right there. Thanks for posting.
Gary

quote Originally posted by GKDINC: That's good info right there. Thanks for posting. Gary

Aaagghhh. Did everything listed above, had such high hopes. Still idles fine when cold (though perhaps a tad low), but can't hold the idle when it warms up.

The only other indicator I have is that the CEL comes on and the code says it's having a problem with the VSS. However, I was told that the VSS doesn't effect idle, and a bad IAC can trigger a VSS code.

Why won't my car idle!!!!