I have an '88 GT.
I have just done a valve job to fix a major compression problem in three cylinders.
But now the engine idles at 2500 RPM.
I see no problems with the EGR tube or the IAC.
I suspect that someone before me messed with the idle stop screww to compensate for the compression problem.
I have read that the screw exists, but I do nopt know where.
Does anyone know?

I don't remember on the V6, but it is hidden by a cap and if that cap doesn't have a hole in it (to punch it out), then I would think the idle wasn't messed with. Are you sure you don't have any vac. leaks? Is the throttle plate closing all the way?

Service manuals
http://www.fieronews.net/fusion/downloads.php

[This message has been edited by jaskispyder (edited 05-16-2011).]

The ECM sets the idle don't mess with the screw... the set screw was used at the factory to set the minimum setting to prevent the plate from binding and the ECM controls the rest. If you have a high idle, your timing is either way off or you have a significant vacuum leak...

With all due respect,
My questions is "Where is the idle screw?".
I understand all of the other issues that have been raised.
Since I have alreaduy looked at those issues, I am trying to see if the screw has been messed with.
Does anyone know where the screw is?

quote Originally posted by sd_iconoclast: With all due respect, My questions is "Where is the idle screw?". I understand all of the other issues that have been raised. Since I have alreaduy looked at those issues, I am trying to see if the screw has been messed with. Does anyone know where the screw is?

Download the service manual (using the link I provided) and this will tell you were the screw is, how to access it and how to reset it.

look at the throttle linkage that the throttle cable goes to. follow that all down to the stop the throttle is resting on. youll see a little bit of something sticking up. thats your idle set screw. directly behind that (probably covered in foil and needs to be punched out) is the head to the screw. its common among most cars and bikes or anything with a throttle blade. but on cars with fuel injection, adjustment is not needed due to the invention of the IAC (idle air control) valve

[This message has been edited by americasfuture2k (edited 05-16-2011).]

It's on the throttle body facing straight up, and if not touched from the factory, it should be covered by a cap.

quote Originally posted by jaskispyder: Download the service manual (using the link I provided) and this will tell you were the screw is, how to access it and how to reset it.

Thanks jaskispyder.
I have the factory manual. I have been unable to find any reference to the idle stop screw in the manual. Can you give me a hint where it is?

There is only one reason this screw would ever need adjustment...and even then, it's because of a worn out part. The screw is used to set "minimum throttle stop". It is not intended to be used for idle settings. The engine computer and all of it's sensors and solenoids take care of the idle speed. If you adjust it anyways, the computer will try to correct what you just did. So you end up fighting with the computer, and it will certainly win.

Try checking for vacuum leaks, clean the throttle body, clean the throttle blade and the idle air control solenoid. If all of that doesn't correct it, check for excessive play in the throttle body shaft. If there is excessive play, the throttle body shaft bushings (and or shaft) are worn and you need a new/good used throttle body.

Edit: I see you posted just before me, saying that the cap is missing. It's possible that the previous owner tried adjusting it to correct the idle. What I posted above still applies, but you might want to go through the procedure of adjusting minimum throttle stop. Then go from there.

[This message has been edited by 1fatcat (edited 05-16-2011).]

I was just looking at a spare TB I have sitting on the shelf. I do not believe that the "stop" screw can be screwed in enough to get the idle to 2500. As said above, it's sole purpose is to keep the butterfly from "sticking" in the bore of the TB. At idle, the plate does not allow enough air into the PLenum for the car to run. Plus, the TPS would tell the ECM that the throttle is "open". I believe you have another issue. Having said yourself that you just did a valve job, I would bet that you have a seal problem with one if not all of the manifilds. Could be the IAC tube itself is either not seated correctly in the TB - I have seen folks do this many times when reinstalling thier TB. You need to make sure that it is seated past the oring inside the TB - or the rubber hose connector on the other end is hard as a rock and is sucking air there. If it idled fine before you did the heads, it's not the TB! Just saying, before you go messing with the stop screw, you would be better served making 100% sure you do not have a vac leak. 2500 idle would be a large vac leak of a lot of little leaks.

quote Originally posted by katatak: Just saying, before you go messing with the stop screw, you would be better served making 100% sure you do not have a vac leak.

I appreciate the advice, and normally I would agree. However, it seems apparent that the idle stop screw has already been messed with. So I am really trying to put it back the way it was.

To add some more info, I did a leakdown test before doing the valve job. All odd cylinders scored about 94%. #2 scored 60%. #4 scored 40%. #6 scored 8%. I have to wonder how it idled at all with numbers like that.

quote Originally posted by sd_iconoclast: I appreciate the advice, and normally I would agree. However, it seems apparent that the idle stop screw has already been messed with. So I am really trying to put it back the way it was.

Just for reference, the engine will idle properly just fine with that screw fully removed and tossed into a wastebasket. Just so you know...

My 85 SE v6 I just got started someone turned the screw and it idled at about 2500 rpms no matter what. Luckily i caught on to what it was in about an hour of troubleshooting it. The screw was also very seized so I had to soak it overnight and then it barely turned. Someone turned it a long time ago.

quote Originally posted by JazzMan: Just for reference, the engine will idle properly just fine with that screw fully removed and tossed into a wastebasket. Just so you know...

With 3 bad cylinders?

Yep - the IAC will open up till the engine is idling at 900 rpm. Pull one of the two INJ fuses and your Fiero will be idling on only 3 cylinders.

The screw is not an idle adjustment screw. It is a throttle stop screw. To adjust it first warm up the engine fully. Then jumper A-B and turn the key on. You will hear a noise from the IAC valve as it tries to fully close. Let this go for about 30 seconds and then unplug the IAC. Then start the engine. You will need to use some throttle to get the engine to start most likely. Then use the screw to get the engine to idle at 500 rpm.

If you can't get the engine to idle down that much you have a vacuum leak.

When done plug in the IAC and restart the engine. The ECM will bring up the idle to 900. Also reset the ECM to clear any SES codes.

[This message has been edited by phonedawgz (edited 05-17-2011).]

well, the above has shown where it is. now - on to what to do with it:
as mentioned - there is no actual "idle" screw. the screw/adjuster sets the throttle closed position. Idle is controlled thru the Idle Air Control. That little hole on the inside bottom of the throttle body, just before the butterfly - also the source of the loud sucky sounds when you remove the air intake rubber snorkle. Now - likely there IS a vacuum leak, or the IAC is stuck open, but - lets go on as if there is not, and this screw actually DOES need to be set. get the car fully warmed up. Cover the IAC hole with your thumb. no, it wont suck the skin off. now, the ECM has no control over the idle. and - if the car is running poorly - it WILL stall. now, adjust that screw to get the engine idling at 500 rpm. remove thumb from hole. that is it.
may want to goose it a few times, then cover the hole again to verify the throttle closing

The way to check the EGR tube is to cut a strip of aluminium can 1 1/2" wide. Then loosen up the upper plenum to EGR tube bolts. Slip the aluminium can block off between the two and tighten the bolts. If that brings the idle down then you have a cracked EGR tube. If that doesn't bring the idle down then most likely you have an out of place IAC tube O-ring.

An easy way to check the EGR tube is to start the car, engine cold. Before it gets too hot, try to wiggle the EGR tube. If you hear a hissing noise that changes in intensity as you wiggle, the tube is bad. If the tube snaps off in your hand while you wiggle, it is VERY bad.

OK, It looks like I must eat some humble pie.
There was a vacuum leak. It turns out that I had not completely tightened down the flange from the EGR tube to the EGR valve.
There was just a small crack. I tightened it down and now I am idling at about 1100 with the ALDL jumpered.
So now I find myself confused abouty how to properly set the timing.
The factory manual does not say explicitly how to set the timing. It just says to consult the "Tune Up" label on the vehicle.
My Chilton manual has a procedure that is obviously wrong. It does not mention jumering the ALDL connector.
The "Tune Up" label says (roughly) how to set the timing, and it says my timing should be 10 degrees BTDC, but it does not say at what engine speed.

download the GM service manual?
http://www.fieronews.net/fusion/downloads.php

quote Originally posted by jaskispyder: download the GM service manual? http://www.fieronews.net/fusion/downloads.php

When I say "Factory Manual", I am referring to the GM Service manual.
The instructions for setting timing are on page 6D4-2.
But, as I said before, they are pretty sparse.

quote Originally posted by sd_iconoclast: When I say "Factory Manual", I am referring to the GM Service manual. The instructions for setting timing are on page 6D4-2. But, as I said before, they are pretty sparse.

oops, sorry, I missed that and read the part about Chilton, so I thought you didn't have the factory manual.

I am guessing that the video I can't see at work is the one that shows you how to set the timing... so nevermind

[This message has been edited by carbon (edited 05-19-2011).]

Setting timing is pretty easy. Start the car and warm it up. Shut it off. Loosen the distributor clamp bolt just enough that you can turn the distributor with some effort. You don't want it too easy to turn because it'll wiggle around and change on its own. Use a paper clip or other piece of conductor and jumper the proper terminals on the ALDL to put the ECM into diagnostic mode. Start the car and adjust the timing to spec, then tighten down the distributor clamp bolt. Shut off the car and remove the jumper, and you're good to go. You must jumper the ALDL because otherwise the ECM commands as much as 40 degrees of advance at idle; it does not use a linear timing curve. If you adjust it without jumpering the ALDL then the base timing will be way off.

I found out you cant adjust the idle with the screw. Soon as you do, then shut the car off, the ECM resets anyway so your back to same idle speed with the idle screw out of adjustment. It dont work like a carb idle screw.

The "idle adjustment screw" is actually a "keep alive" adjustment, in case the IAC should fail. With the IAC forced closed, it should be adjusted for 600 RPM.

If the car is idling that high look under the throttle body and they is a hose or pipe that connect to the throttle body

Hey Guys,

My car has a bored throttle body and the adjustment screw cap was gone when I got it back.
I also know for fact that I messed with it thinking it was an idle adjustment when I was trying to get my car back up and running.

Car runs great now and idle through the ECM is steady at 900RPM so I see no issues there.
Just curious about what the idle speed should be if I cover up the IAC port? I see 500 mentioned and then 600?
My car is a 4-speed manual.

Can someone confirm what the idle speed should be with IAC blocked so I properly check the setting on the screw?

Cheers

See my Cave, Idle Stop