minimum idle
Thread Starter
Pro
Joined: Apr 2006
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From: Perth Western Australia
minimum idle
i tried to set the minimum idle the other night.
i have about 3 sets of instruction from different places and they all say pretty much the same thing.
i followed the instruction as close to exact as possible, but after the est and iac was disconnected i could not, at all get the car to idle.
it would start.... and run if i gave it some gas, but stalled when i took the foot off the break.
am i meant to start the car before i start disconnect these things? or was i right in disconnecting first, then starting (as im pretty sure the instructions say)
thanks
i have about 3 sets of instruction from different places and they all say pretty much the same thing.
i followed the instruction as close to exact as possible, but after the est and iac was disconnected i could not, at all get the car to idle.
it would start.... and run if i gave it some gas, but stalled when i took the foot off the break.
am i meant to start the car before i start disconnect these things? or was i right in disconnecting first, then starting (as im pretty sure the instructions say)
thanks
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
After disconnecting the iac, srew the set screw in a few turns, this will allow the car to idle so you can get back under the hood. Then back it down to 450 rpm or whatever the spec is. I don't mess with the est.
Le Mans Master
Joined: May 2005
Posts: 5,214
Likes: 65
From: Queensland, AUSTRALIA
Yeah your screw was probably too far out, so it couldnt get enough air to idle.(do the said sequence, then start it, turn your screw up a fair bit first if you want, it wont hurt, then just wind it out til its down to the following....>) As soon as you set it to 400rpm in Drive (if its auto, if not its 450 in Neutral as CentralCoaster said) its done, it should idle at that with the IAC unplugged, when you plug that back in and start it again it will be perfect (or should be) Do the TPS after you set the minimum airflow screw. 
(you dont remove the EST plug for this procedure)
(you dont remove the EST plug for this procedure)
Thread Starter
Pro
Joined: Apr 2006
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From: Perth Western Australia
Yeah..... i was getting mixed reports about the est.... some say disconnect, others dont??
ill try screwing it out a little further then starting the car without the iac. see if i can get the car to idle by itself
ill try screwing it out a little further then starting the car without the iac. see if i can get the car to idle by itself
Le Mans Master
Joined: May 2005
Posts: 5,214
Likes: 65
From: Queensland, AUSTRALIA
Nah mate, leave it plugged in. I did it on my 87 when i had it and i never unplugged it. When i did mine it was idling way too high, someone had screwed the minimum flow screw all the way in before i bought it. So that made it really easy for me to get the car to start after the initial sequence. Youll think some one is having you on about the idle speed during this, but when you reconnect and restart it will be fine!! 
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Le Mans Master
Joined: Feb 2005
Posts: 5,146
Likes: 3
From: The Motor City
Originally Posted by Casethecorvetteman
Mine wasnt, and i had no issues.
The position of the IAC is calculated by the ECM based on battery voltage, coolant temp., engine load, and RPM. The chip should have: idle (engine RPM)based on temp, and IAC position(counts)to temp. programed/programmable in it.
I think setting it at a colder temp. (higher idle rpm)would produce an undesirable result, as the idle speed would change (lower)once the car is at Operating Temp and in closed loop.
Instructor
Joined: Apr 2005
Posts: 138
Likes: 0
From: 86 Convertible 4+3 Coronado, CA
I followed the tech tips procedures here in the forum last weekend and had no problem. Left EST alone...see Vader86's homepage for some additional details. As mentioned above, you'll need to reset TPS after you've finished with IAC.
You can hear the idle drop as you turn the screw with IAC unplugged. However, at one point, I was backing the screw and heard no drop in idle. I turned it some more...still no change. Then I rocked the throttle by hand to rev it, and when it reset it dropped the idle way down. Be alert for the throttle cable hanging up as you back the idle screw out...rock the throttle by hand every time you finish turning the screw to make sure it is seated against that screw.
Good luck!
You can hear the idle drop as you turn the screw with IAC unplugged. However, at one point, I was backing the screw and heard no drop in idle. I turned it some more...still no change. Then I rocked the throttle by hand to rev it, and when it reset it dropped the idle way down. Be alert for the throttle cable hanging up as you back the idle screw out...rock the throttle by hand every time you finish turning the screw to make sure it is seated against that screw.
Good luck!
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 32
From: The Top of Utah
Originally Posted by mseven
I think setting it at a colder temp. (higher idle rpm)would produce an undesirable result, as the idle speed would change (lower)once the car is at Operating Temp and in closed loop.
I agree that it is best if the engine is warmed up, because the engine will be happier idling slowly and the ECM can adjust the mixture appropriately.
RACE ON!!!
Thread Starter
Pro
Joined: Apr 2006
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From: Perth Western Australia
yep, cars was warmed up.....
just clarify, im here without any of my stuff(info sheets on how to do this).
closed loop? is that with the a' b' terminals conected? or not connected.
cos i did as the instructions said, i removed the loop between termnals a' and b' before i started the car with the iac disconnected.
someone many moons ago said you should leave the a' b' loop connected.... but i sounded dodgy to me.
just clarify, im here without any of my stuff(info sheets on how to do this).
closed loop? is that with the a' b' terminals conected? or not connected.
cos i did as the instructions said, i removed the loop between termnals a' and b' before i started the car with the iac disconnected.
someone many moons ago said you should leave the a' b' loop connected.... but i sounded dodgy to me.
Race Director
Joined: Sep 2000
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From: The Top of Utah
Originally Posted by ozvette87
closed loop? is that with the a' b' terminals conected? or not connected.
1. Warm the engine.
2. Ignition "Off, engine "Off". Jump terminals "A" and "B" of the ALDL together.
3. Turn ignition to "On".
4. Wait 30 seconds, then unplug the IAC connector.
5. Turn the ignition "Off".
6. Remove the ALDL jumper.
7. Start the engine and adjust the minimum air to the specified (desired) rpm.
8. Shut off engine, connect IAC.
9. Ignition "On", adjust TPS voltage.
10. Acclimate the IAC. Some cars have an ignition on/off procedure, but it will happen on all C4s, if you take it, warmed up, for a drive and exceed 40 mph.
Apparently, some year FSMs say to disconnect the EST wire. Most *I* am aware of don't. If the manual says to disconnect the EST, then disconnect it.
RACE ON!!!
Last edited by CFI-EFI; Aug 3, 2006 at 07:35 PM.
Thread Starter
Pro
Joined: Apr 2006
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From: Perth Western Australia
ok, thanks.... that is the most common of the two versions ive heard... so im taking that as gospel from now on
ill try what case said and turn the screw in/out (depending how you look at it) a cople of times and see if i can get the car to idle. thanks for the reasurance and help people
ill try what case said and turn the screw in/out (depending how you look at it) a cople of times and see if i can get the car to idle. thanks for the reasurance and help people
Le Mans Master
Joined: May 2005
Posts: 5,214
Likes: 65
From: Queensland, AUSTRALIA
Originally Posted by mseven
I think setting it at a colder temp. (higher idle rpm)would produce an undesirable result, as the idle speed would change (lower)once the car is at Operating Temp and in closed loop.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 32
From: The Top of Utah
I agree, but...see post #12. Colder engines need a faster idle and a richer mixture than a warm engine. The ultra slow minimum air idle speed will be more stable in a warm engine and with a mixture suited to that warmer temperature.
RACE ON!!!
RACE ON!!!
Melting Slicks
Joined: Apr 2002
Posts: 2,118
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From: St. Charles, MO Route 66 Corvette Club
I know all C4 years are different. As for the connecting or disconnecting the EST, here is the wording in my 89 GM Helms manual:
IMPORTANT: The distributor set-timing connector must be disconnected to fix spark-advance at base timing. This eliminates the possibility of changes in engine speed due to changes in timing.
I think the ECM will attempt to reach the desired RPM by changing the timing.....as far a possible. When you set the RPM in this condition, I do not think you have set the base idle correctly. My opinion! I have attempted to set my base idle with and without the EST connected. The best result on my 89 was with the EST wire disconnected. Hope this is helpful!
IMPORTANT: The distributor set-timing connector must be disconnected to fix spark-advance at base timing. This eliminates the possibility of changes in engine speed due to changes in timing.
I think the ECM will attempt to reach the desired RPM by changing the timing.....as far a possible. When you set the RPM in this condition, I do not think you have set the base idle correctly. My opinion! I have attempted to set my base idle with and without the EST connected. The best result on my 89 was with the EST wire disconnected. Hope this is helpful!
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
I have an note from Killebrew on the procedure. It's published many other places in many different ways, and his is the best explanation. CFI's post is correct. Killebrew mentions the EST and putting it in park vs drive vs neutral, I forget the details. Basically all those, and engine temp effect the idle speed.
Although you can leave the A+B jumper in there and start it, when the SES flashing changes it's in closed loop.
Although you can leave the A+B jumper in there and start it, when the SES flashing changes it's in closed loop.
Thread Starter
Pro
Joined: Apr 2006
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From: Perth Western Australia
most things i read with instructions on linking a' b' terminals on the aldl say Not to start the engine. i have personally seen it started with the terminals linked and all that seems to happen is the ses flashes really fast.
why is it so bad to start the car with the two terminals linked?
why is it so bad to start the car with the two terminals linked?