darkred87T
Active Member
- Joined
- Oct 27, 2003
Does anyone know what setting the idle adjustment screw (behind the throttle) is supposed to be set at for an 87?
Idle adjustment screw
- Thread starter darkred87T
- Start date
It's not an idle rpm adjuster. It sets "minimum air bleed". The chip controls idle rpm electronically, and is uses the IAC device under the throttle body to do so.
There is a range of IAC values that seem to work best on these vehicles (depending on how radically modified they are) and that's usually anywhere from 10-30 (keeping in mind the tps must also be re-adjusted to spec anytime there's an adjustment to IAC).
Now, back to that screw. It changes/adjusts the IAC numbers (as seen on a scan tool) if they're out of spec for whatever reason.
Turning the screw CW reduces the IAC counts, and turning CCW increases them.
This adjustment should NEVER be attempted without a scan tool than can monitor IAC counts.
There is a range of IAC values that seem to work best on these vehicles (depending on how radically modified they are) and that's usually anywhere from 10-30 (keeping in mind the tps must also be re-adjusted to spec anytime there's an adjustment to IAC).
Now, back to that screw. It changes/adjusts the IAC numbers (as seen on a scan tool) if they're out of spec for whatever reason.
Turning the screw CW reduces the IAC counts, and turning CCW increases them.
This adjustment should NEVER be attempted without a scan tool than can monitor IAC counts.
Just to clarify....
...it is a throttle hard stop, and aside from adjustment, it's purpose is to keep the throttle blade from binding up in the throttle bore from closing all the way. It doesn't actually set IAC, the ECM does that based in the motor's needs. The throttle hard stop setting will affect the amount of air entering the motor at idle (bypassing the throttle blade) , thereby affecting the IAC counts. Any adjustment of the throttle stop will require readjusting the TPS as well.
...it is a throttle hard stop, and aside from adjustment, it's purpose is to keep the throttle blade from binding up in the throttle bore from closing all the way. It doesn't actually set IAC, the ECM does that based in the motor's needs. The throttle hard stop setting will affect the amount of air entering the motor at idle (bypassing the throttle blade) , thereby affecting the IAC counts. Any adjustment of the throttle stop will require readjusting the TPS as well.
Re: Just to clarify....
Ummm, nope, sorry, it is in fact the Minimum Air Bleed adjustment, which is used to calibrate the IAC if and when it's replaced or needs calibration(you might want to check the service docs). Is was not designed to be a throttle stop screw, that could easilly be accomplishe with any non adjustable nib.
Originally posted by Rickracer
...it is a throttle hard stop, and aside from adjustment, it's purpose is to keep the throttle blade from binding up in the throttle bore from closing all the way. It doesn't actually set IAC, the ECM does that based in the motor's needs. The throttle hard stop setting will affect the amount of air entering the motor at idle (bypassing the throttle blade) , thereby affecting the IAC counts. Any adjustment of the throttle stop will require readjusting the TPS as well.
Ummm, nope, sorry, it is in fact the Minimum Air Bleed adjustment, which is used to calibrate the IAC if and when it's replaced or needs calibration(you might want to check the service docs). Is was not designed to be a throttle stop screw, that could easilly be accomplishe with any non adjustable nib.
darkred87T
Active Member
- Joined
- Oct 27, 2003
Thanks, when I first got the car, it seemed to idle rough and not knowing any better I turned that screw to raise the idle not knowing that it could mess something up. I thought someone might know for instance how many turns in that screw should be to get it back to the factory setting.
You can't guess at some like that, but a good baseline is something like this: take a look at the part of the screw that sticks out the front where it's supposed to touch the throttle, you'll notice the end has no threads for a short distance. Try to adjust it so that there is only about half the firts visible thread is showing on the front there.
BUT, and it's a big BUT, make sure you remember that ANY adjustment in that screw means you'll have to re-adjust the TPS.
darkred87T
Active Member
- Joined
- Oct 27, 2003
Thanks, I'll try that. Maybe this is the reason why i'ts stalling when I'm driving?
turbojimmy
Supporting Member
- Joined
- May 26, 2001
We have Directscan hooked up to it (darkred87t is my brother) but I don't remember what the IAC counts were. We'll have to look again. The engine is freshly rebuilt, but it has always run this way. We swapped out the O2 sensor, IAC valve and MAF sensor. Both the IAC valve and MAF were used off of my car (had about 80k miles on them). The O2 sensor is a new Delco.
The idle seems to be too high when it's cold and then too low when it's warm. So low that when you get off the gas real quick it will sometimes stall. Smells rich too.
Checked for vacuum leaks but didn't find any.
Jim
The idle seems to be too high when it's cold and then too low when it's warm. So low that when you get off the gas real quick it will sometimes stall. Smells rich too.
Checked for vacuum leaks but didn't find any.
Jim
- Joined
- Jul 20, 2001
Another term for the screw is minimun idle set screw. It will allow the engine to idle even if the computer is not controlling idle speed. If you don't have a scan tool, there is a primative method to set it. Ground the ALDL connector (to keep new codes form setting) and key on engine off (KOEO), for around 20 seconds. With KOEO, disconnect the idle air control (IAC) motor. This takes the IAC out of the equation. Start engine and it will be at a really slow ilde speed. Using the a screw driver to move the minimum air bleed screw, set the idle speed to 450 rpms in drive. This will be the set point for the minimum air bleed screw. Turn engine off, reconnect the the IAC connector and remove the connector between the a-b pins of the ALDL. Verify the TPS setting is at spec and start engine. Idle speed will again be controlled by the ECM and rise to the appropriate level.
turbo nasty
Turbo Dojo / MNTR
- Joined
- Jul 19, 2001
Min air blade setting
gofstbuick, thank you
I was going to look up the procedure again and post it, but it was another extremely busy day at the shop. What you posted looks pretty close to a "by the book adjustment", which is what I was referring to. You're not supposed to set IAC counts via the throttle stop screw, you set minimum idle first, then TPS, and IAC counts should fall in line, if they don't, something else is wrong.
I was going to look up the procedure again and post it, but it was another extremely busy day at the shop. What you posted looks pretty close to a "by the book adjustment", which is what I was referring to. You're not supposed to set IAC counts via the throttle stop screw, you set minimum idle first, then TPS, and IAC counts should fall in line, if they don't, something else is wrong.
Re: gofstbuick, thank you
Yes, assuming you're "going by the book" using mid 80's vintage shop proceedures, that were written in very generic terms and had to be able to be accomplished by all manner of GM shops, even those that didn't have the luxury of an active scan tool (of which there were many back then!).
Today, things are a bit more modernized.
Originally posted by Rickracer
I was going to look up the procedure again and post it, but it was another extremely busy day at the shop. What you posted looks pretty close to a "by the book adjustment", which is what I was referring to. You're not supposed to set IAC counts via the throttle stop screw, you set minimum idle first, then TPS, and IAC counts should fall in line, if they don't, something else is wrong.
Yes, assuming you're "going by the book" using mid 80's vintage shop proceedures, that were written in very generic terms and had to be able to be accomplished by all manner of GM shops, even those that didn't have the luxury of an active scan tool (of which there were many back then!).
Today, things are a bit more modernized.
I use the most up to date software...
...not a mid eighties Motor manual, and I've been wrenching on cars since before I was old enough to drive. I am one of the best driveability technicians in Osceola county, (see sig.) I didn't say by the book was the only way, I was merely pointing out that using the screw to set IAC counts might possibly cause overlooking another problem. There is more than one way to skin a cat, some more efficient than others, some more thorough than others.
...not a mid eighties Motor manual, and I've been wrenching on cars since before I was old enough to drive. I am one of the best driveability technicians in Osceola county, (see sig.) I didn't say by the book was the only way, I was merely pointing out that using the screw to set IAC counts might possibly cause overlooking another problem. There is more than one way to skin a cat, some more efficient than others, some more thorough than others.
turbojimmy
Supporting Member
- Joined
- May 26, 2001
Okay, I've been driving the car for a week (the darkred87t). I sold my daily driver and am using this T in the meantime.
Whatever you want to call that little screw, I reset it today. IACs were in the mid-40s so I turned the screw in clockwise until they got down to around 15. Also, before I messed with the screw I noticed that the TPS was only 36. I adjusted the screw, then set the TPS at 46. I can't get the TPS anywhere near 4.5 @ WOT though. I'll fix that later.
Drove the car around a bit. The stumble and hesitation is gone. Idles nice. Once it warmed up IACs dropped to 6? Not sure why. I may need to mess with it some more.
When it's cold and doing the programmed fast-idle to warm up it has an obvious miss. When it goes to closed loop the miss goes away. Not sure if it's related to an electrical problem, but the tach is all goofed up. It worked fine before, now it works at random and when it does work it's just a fit of lights - not really an indication of RPM.
I think the car runs awesome, but my brother is pretty picky.
I'd like to get to the bottom of the miss.
Jim
Whatever you want to call that little screw, I reset it today. IACs were in the mid-40s so I turned the screw in clockwise until they got down to around 15. Also, before I messed with the screw I noticed that the TPS was only 36. I adjusted the screw, then set the TPS at 46. I can't get the TPS anywhere near 4.5 @ WOT though. I'll fix that later.
Drove the car around a bit. The stumble and hesitation is gone. Idles nice. Once it warmed up IACs dropped to 6? Not sure why. I may need to mess with it some more.
When it's cold and doing the programmed fast-idle to warm up it has an obvious miss. When it goes to closed loop the miss goes away. Not sure if it's related to an electrical problem, but the tach is all goofed up. It worked fine before, now it works at random and when it does work it's just a fit of lights - not really an indication of RPM.
I think the car runs awesome, but my brother is pretty picky.
I'd like to get to the bottom of the miss.
Jim
turbojimmy
Supporting Member
- Joined
- May 26, 2001
Okay. The car stalled on me today. Backfired through the intake yesterday My brother was telling me it stalled at random, but I'd never experienced it. Crusing in stop-n-go traffic on Rt. 80 and give it some gas and realize the idiot lights are lit up. It had stopped running at some point (ahhhh the joys of a stock exhaust - can't even hear it run).
Another weird thing is that the IAC counts are now 0. When I stop and put it in park they immediately count down to 0. I also noticed that when you wind it out it falls on its face. Like it hits a wall at higher RPMs. Smells rich. I'm thinking maybe MAF.
Does the MAF come into play in open loop? Or just closed? When it's cold it's missing, but my car does something similar but not as bad.
Any ideas would be appreciated.
Jim
Another weird thing is that the IAC counts are now 0. When I stop and put it in park they immediately count down to 0. I also noticed that when you wind it out it falls on its face. Like it hits a wall at higher RPMs. Smells rich. I'm thinking maybe MAF.
Does the MAF come into play in open loop? Or just closed? When it's cold it's missing, but my car does something similar but not as bad.
Any ideas would be appreciated.
Jim
TTT because I am curious about the IAC being 0.0 also. I re-adjusted mine today. I "thought" the car was warmed up, but after driving it back home tonight (about 25 miles) I put it in park in the driveway and the IAC was 0. Car idled and ran fine, but I'm just curious how essential that 10-30 is.
TIA
TIA
darkred87T
Active Member
- Joined
- Oct 27, 2003
Very frustrating, there must be an obvious problem we are overlooking.
