slickfx3

this was not a problem until the other day it went from 1300 to 1700, it's high.

i cleaned the IAC (it was filthy) and it helped the drive-ability and even the idle, most of the time, so there is an improvement, but when it wants to stall ( sometimes, i don't know why) it's kick in the stall saver( i think) and brings it to 1700 yet again very erratic but only if it wants to stall.

does PID IAC warm park steps v. coolant temp set higher make this condition go away?.

over at corvette forum, it is agreed that the ecm are tuned that way and is call throttle follower logic or something like that.

Comments please

RBob

iTrader: (1)

On the '7165 MAF ECMs it is important to set the minimum air followed by the TPS voltage. Try that first and see if it helps out. If the IAC was that dirty also clean the throttle body and blade. Do this before hte above settings.

It may also be that the IAC is still sticking. That causes havoc with the idle speed.

Noting the mini-sig, that set up will require some tuning to get it right.

RBob.

slickfx3

i cleaned the plates and body, i don't really understand how the sooton the plates can affect drivability? the body was out for the engine rebuild and i clean it then, it did get dirty in the backside though.

can you link me to the min air setup please?

1tpi

Go here https://www.thirdgen.org/tpimod2

slickfx3

thanks, my engine has a cam, so what would minimum air be?

1tpi

Your idle rpm will be what's
programed in the chip.

slickfx3

well i thought the minimum air is somewhat lower than the idle vs. coolant, and plugging the IAC back in after setting the tps, will make up the difference...

1tpi

Did you read this, if so read it again:

slickfx3

Start engine. You are now going to adjust "minimum air". There is a Torx screw on the side of the throttle body. This is what needs to be turned to adjust minimum air, or more commonly known as "idle speed". It comes from the factory with a protective metal cap over it. If the cap is still there, use a small punch to knock it out. Set the idle speed to 450 rpm, rotating the Torx screw clockwise to raise rpm, and counter-clockwise to lower rpm. Once the idle rpm is set, turn off the engine.
Re-connect the connector onto the IAC. Start engine. Idle speed is now once again governed by the ECM, but your idle should be smooth and steady, approximately 600 rpm in Drive (for unmodified cars).





read the part about setting it at 450 and the ecm will govern it to 600

UNCLE TOM

iTrader: (1)

the most simple solution is often the best . check/clean/re-lube all pivot points of the linkage to TB . not trying to be a smart a$$ but it happened to me . good luck .

???

iTrader: (5)

I have a SD car not maf but my car has done this forever and I could never find it. its only after starting it, I have to sit and wait stopped for it to idle down to the real idle speed, if I don't wait while stopped it will hang up there all day while driving untill it stop long enough for it to idle down, then its fine till a restart. I think your seeing the same thing but your almost stall is the same as restarting, I've noticed that too since I have a stick and have almost stalled it before and it does it till I sit long enough to idle down again. fix the stalling and it won't bother you as much, but I'm no help at all at fixing it. all I ever noticed is if the vss isn't hooked up it doesn't do it, so I figured it mph based. I think how it holds the revs up a bit while rolling to save stalling under hard braking. something weird in those setting.

dimented24x7

iTrader: (2)

Part of it may also be how the idle and throttle follower routines work. As long as the car is in motion, the engine is not considered to be idling. Because of this, there will be no closed loop control of the engine speed and the min throttle follower airflow will be present as long as the car is moving, which can cause a high idle when your driving and the clutch isnt engaged. The end result is that the RPMs hang until you come to a stop, after which the ECM takes control of the idle again. The only real solution with some of the cals is to decay out the min throttle follower airflow as the car comes to a stop, so the engine will smoothly idle down rather than hang, but GM has never included this in any of the cals as far as I know. Ive had to actually add this into the code of all my PCMs so the idle smoothly comes down as I come to a stop rather than the hang and suddenly drop.

slickfx3

i have heard it is designed to behave like that, as you have said

yeah but it was fine when it was only 1300 rpm now it goes to 1700+

dimented24x7

iTrader: (2)

How did you clean the IAC? Did you remove the pintle fully for cleaning, or just spray it with cleaner? There is an exposed bearing at the back that just has lithium grease in it. If you use solvents or spray, dirt can be carried into the bearing and/or the grease removed, causing the stepper to bind. Also, did you relube the pintle shaft? That can cause it to stick as well. From my experience, sometimes its better to just replace the IAC if its old and cruddy.

slickfx3

no one ever explain the cleaning that way, they just said clean it, i even soaked it in wd 40 for a while, i did not removed the pintle, don't know how,

bottom line i did not balance and blueprint the iac

DOES THIS issue sound like the IAC to you? SHOULD I change it just for the sake of changing it, it seems to have gone through the base idle adjustment with flying colors

IAC behaves i think okay as per base idle setting procedure.

i read the volts on the tps and it only goes to 2.60 volts and i can read every little movement up to that point,

funny thing is i used an old school needle meter and tested it on the battery fine and when i go to test the tps no readings

i test it with a digital and in reads, what gives?


the tps seems fine and is adjusted to .54volts

i cleaned the IAC and cavities

cleaned throttle body front and back and removed air foil.


the car still idles high when moving in closed loop when hot and if i drive it spirited, if i putts, it idles normally occasionally.

i checked the linkage for binding, has play in it (lots)132,xxx miles, but no binding

the idle does settle back down when stopped

but it can go to 1700-1800 while driving and coasting in neutral.

CAN the worn shaft make the idle high and the ecm brings it down when stopped?

it was old and cruddy, but here is is cleaned, but not your way...

dimented24x7

iTrader: (2)

Its hard to say if the IAC should be changed, but its not a real expensive part, so it cant hurt. My original IAC had a tremendous ammount of carbon, much of which had made its way into the body and caused the armature to stick in certain places. The ECM does not know where the IAC actually is, so if it sticks, this can cause the idle to behave erratically as the ECM thinks the IAC is in one place, but its really stuck at another. This is why its important that the IAC not miss any steps.

The throttle body could also do it. When they wear like that, the shaft typically wears off-center due to the loads imposed on it, which causes the butterflies to bind in the bores. It will feel fine when the engine is off, but under vacuum, the shaft is pulled off-center, which can cause the throttle to hang open, causing a high idle. FWIW, the load on the throttle shaft from vacuum alone can be over 50+ lbs for large TBs, which is why they wear so much.

If its really sloppy, then you should have it re-bushed. That will help alot there as it will ensure that the throttle will close fully all the time. My old stock TBI had these same issues. It would constantly hang open, causing a high idle.

tequilaboy

You have too much air with your current warm park position table plus the manual transmission offset (typically 5 counts offset).

Either reduce the throttle opening, or reduce the warm park position table settings so they will provide reasonable airflow while coasting down off throttle and out of PID.

Another option would be to raise the PID velocity threshold to allow PID control above 1.8 mph. I've gone as high 15-20 mph with PID control so I can idle in 3rd gear and have a pseudo low speed cruise control.

slickfx3

throwing parts at a car is something i have tried to abandon since highschool (1973-76) but is there is no accurate manner to troubleshoot the part, i may consider it,

it started out of nowhere, and it could be the combination of both issues, the throttle shaft is awfully loose, but to it's credit the idle will go back to normal at stop, and this is inverse of the vacuum holding the plate ajar, since vacume goes up as rpm goes down, correct?

it seems like its either one or the other or even both, i have a stock 48mm,TB for a cammed up 383, so going up to 52 is something i had slated for the future, not now, apparently the symptoms are rushing me into this expense.

I'll check the parts for sale section

Does the IAC compensate for the smallness of the TB?, to rephrase; because it was appropriate for a 350 until I threw in a wild 383, that's a roughly 10% more air requirement at any given RPM, not factoring heads, cams, efficiency,etc

Or at the very least open up more for any given rpm? This theory would give a reason at to why it would stick at a point beyond what that particular unit was accustom. in all case thanks for the insight. and a swapping we will go...

slickfx3

I have been looking for this answer for days, i have even seen you post to something to they affect on similar problems pose by others however you did not elaborate and now you have.

what doe pid stand for?

http://www.expertune.com/tutor.html

am i trying to mask a mechanical problem with a software solution?

my idle hanging is a false cruise control at times, albeit unpredictable, too fast and Micky mouse

i'll open up tuner pro and report the affects thanks, better than buying parts for now anyways....

Ericc

Proportional–Integral–Derivative

It's a control process whose origin is in the analog world but made the transition into the modern digital age. New digital control methods are better but not seen in older ECU's.

Everything you ever wanted to know about PID control and loops:

http://en.wikipedia.org/wiki/PID_controller

Eric

dimented24x7

iTrader: (2)

The IAC will not open any more when you have a smaller TB or a large one when driving. When your driving, the ECM is not in closed loop idle. It just moves the IAC a fixed ammount based on how many throttle follower steps are commanded, which is why it could be an IAC problem as the IAC will move to allow throttle follower airflow, but not retract back down if its sticking. Once you go back into closed loop idle, the ECM will basically step the IAC until it moves. You could check it by unhooking the IAC while the engine is idling and then drive the car again. If the problem goes away, then its a good chance that its the IAC.

dimented24x7

iTrader: (2)

DO NOT play with the PID settings at this point and time if the problem just came out of the blue. The early ECMs are pretty bare bones from a closed loop control stand point, but if your not familiar with how it works, you can do more harm than good by possibly causing idle surging and so fourth.

This is most likely a mechanical issue with the TB or IAC. Rule those out first before trying to tune around it.

slickfx3

thanks, but as per my last post about the moates chip extender, it was the reason the car behaved so poorly, i took it off and Craig okay'd the return and the car runs great!

Thanks for your input!

Curious_George

I am having the same problem with an '87 Camaro (305, A4, stock). The IAC is new, TB cleaned, no vacuum leaks, new gaskets, etc. The TB shaft appears to be OK (very little play). The stock bin (ACXT/32B) has only a slightly high idle at times, where the '89 bin (APYM/6E) seems to make it much worse (9th injector unplugged). I have been fine tuning the ACXT bin and it seems to be running great except for the high idle occasionally. The APYM bin is running good too, but the high idle is much more pronounced, so I went back to the ACXT bin.

I am using TunerPro and I do not see anything in the 32B or 6E definition files for "throttle follower", etc. Please expand on this.

CG

corvair_nut

I have been looking for this forever and finally found it under "upper MPH limit for closed loop idle" It was set for 6 MPH and would not idle down until I got lower than that. I changed this to 15 MPH and I think that is about right.

I would have never found the answer without this forum. Thanks everyone.