Anyone care to shed some lite on these for me? When cold/open loop(first start) it will settle down to idle rpm at a lite/stopsign on after a prolonged delay and more or less stay that way until it enters closed loop and iac learn control settles in. been playing with the "steps" tables but have not really gotten any results. Otyherwise cold/open loop driveability is much improved on my combo(got cold and i've been playing). Im just kind of stuck at this point :-( Have the same thing occuring with the idle flair up on startup, not sure what else to do or what to play with other than the "steps vs." tables? This occurs when hot and cold, have the iac park at 130 and not really wanting to lower it more because i dont want to affect anything else..... All Blm's are in the 120's and i have a fairly decent timing table worked out... Any hints/clues or the blatantly obvious that i am overlooking? thanks as always Jeremy

I've been playing with the idle also.
Something I found is the IAC park position appears to be just that. The position the IAC drives to when you shut off the key.
If you run winaldl just watch the sensor page when you turn the key off. The IAC will drive to the 140 or what ever you set it too.
So it shouldn't have any effect on how the car runs.

My problem is once the motor warms up and I return from a drive. When I put the car in park the idle will be about 200 rpm higher than I have set in the desired closed loop idle speed at 650.
If I put it back in gear it will go right down to 650 and stay there till I go back to park. Maybe it's going to open loop idle or maybe the IAC is sticking?? Still playing with it.

If I turn it off and restart it, it will idle right at 650 in gear or out of gear.

Mechanically speaking, that sounds about right to me. Put it in PARK, idle goes up...put it in gear...larger load on engine (engine trying to drive fluid through torque converter/front pump/trans cooler) without any fuel compensation...idle RPM's go down. Now, with a manual tranny, all bets are off because the engine doesn't have a load with a clutch disengaged. Maybe look at low end stuff like low TPS% or the like...IAC Steps at idle...
Just my $0.02....

Bill, What are your IAC counts at idle, in gear and in park? If they are real low, you may have the minimum idle set too high (Throttle stop screw) Also, is the ecm seein the P/N signal? There are other thing that I think it can be in the bin, but these are the basics to start with.

I am curious about the car with the high idle in park. What is the IAC count in drive, and in park? It wouldn't happen to be 0 in park would it? It can't go any lower than that. Maybe you have a vaccum leak that doesn't show up until the engine is warmed up fully? In gear the engine is loaded, and would lower the engine speed even with a iac count of 0. I guess what I am trying to say is take a good look at the iac counts.

Marcello

The idle code is designed to compensate for the load of the TC, and so the system shouldn't die when Drive is engaged.

John

Yes I agree the idle code is designed to compensate. But what about if the base idle speed is higher than the desired idle speed? The computer would try and compensate, but would dead stop at an iac count of 0. When you are in drive the load might be sufficient to bring the desired back into a range where the iac can become active, but not when in park. At my shop we set GM cars up for an iac count of 30-50 in drive. And that seems to give very good results. Now if someone goes and puts the wrong pcv valve in with a higher flow you can end up with a count of 5 in drive, and a count of 0 in park - never reaching the desired idle while in park. Or there is a vacuum leak. Or is the base idle stop just wasn't set right. I've seen people try and set the base idle with the throttle stop - which would give exactly the results of higher idle in park. Instead of setting the throttle stop so the computer can control the idle speed. Just an idea.

Marcello

The IAC counts are 44 in gear with the rpm about 850. When I put it back into drive it holds just about the same.
If I shut it off and restart the IAC is about 37 when the motor settles back down.
I will reset the blade angle and the TPS. I have the TPS at 1.7% right now at idle and it may be causing the problem. IIRC winaldl list 0% right at .48vdc.

Next question?
What table do you use to adjust the cold fast idle?
Target Idle only goes down to 55*C.
I know I'm missing the obvious....

Thanks.

Some ECM's/MaskID's don't do a closed loop idle control while in park/neutral.

RBob.

Which car (ECM/Mask) are you working with?

RBob.

Just out of curiosity Rbob what does the 747 ecm with the 42 mask do for idle, Since my setup is a swap in a non stock chassis I didn't bother hooking up the PK/N switch. Winaldl just shows pk all the time. I'm starting to get the VE tables in the ball park and really need to get the idle smoothed out.

Needs to be in drive for closed loop idle control. If you left the Pk/Neut wire open then the ECM will see in-drive. Pin B10, typically orange w/black stripe.

RBob.

Intresting, actually I hooked up the wire to the stock switch only it is no longer hooked up because of the aftermarket shifter. I can rotate the stearing column and make it go into drive so I may have to try that on the way home. Is there any side effects to leaving it in "drive"?

On stick shift vehicles the wire is left open for drive, all of the time. On an auto w/o the pk/nt switch I think it is better to leave the wire open. This will give better idle control.

With a system where the pk/nt switch is connected the ECM adds steps when the trans is shifted into drive. This helps prevent stalling.

If not using the switch you can also fudge the throttle stop screw setting. Set it a tad high for pk/nt with 0 IAC steps. Then when dropped into gear the idle comes down along with having IAC steps due to the increased load.

RBob.

Rbob

ITs the Formula, with the 730 ecm(for now) mand the $8d code.............just driving me nuts thanks
later
Jeremyt

Wow much better idle now, I'm still getting the IAC counts to cycle out and "stick" at 145 after it warms up but it takes much longer for it to do that now. I'm still trying to get the blm's in the ball park after the last fuel pressure adjustment. Once I get everything close it would idle pretty decent but not really at the determined rpm in the chip, this explains why. It only sticks at 145 when the tunes way off.

OK, I think I have an idea for the startup flare and how the IAC operates. Hook up a scan tool and have it display the IAC steps. With the engine running and then shutting it off, the IAC steps should go to the park steps at L8629.

Wait 10 seconds then key on (don't start engine). The IAC steps will go to a position for startup. This shouldn't be the same number of steps as the park position. If it does it may just be due to luck.

This warm start park position is built from a couple of input terms. The base is the learned idle steps. This is developed while the engine is up to temperature and running. It is then stored by the ECM for the next key on (if the battery is disconnected all this goes away and defaults are used).

Added to this learned base value is the steps from the table at L8689, WARM PARK POSIT vs COOLANT.

Added to this value is the steps from the table at L86A1, IDLE SPEED TIME OUT IAC STEPS vs COOLANT or MAT.

Those three values added together make up the warm start IAC position. The time-out steps from L86A1 decay out as the engine is running. These need to decay to zero before an idle learn takes place (along with two coolant thresholds).

Now, disclaimer time, I only went through the code for this. So it may not be entirely correct. Give it a try and see what happens.

The startup IAC position tables can be played with and checked w/o even starting the car. I would make some large changes to the two tables and see where the IAC goes at key on. This should verify if I got the code correct.

It also looks like if the A/C is requested at key on there are additional steps added. Keep this in mind if the heater controls are on defrost or A/C position.

RBob.

You're on the right track. The settings between the throttle plate angle, TPS, IAC counts in the table all have an effect. Sounds like at least your TPS and IAC are where I would want them to be. The largest change I have found in the flare up upon starting is the start up fuel. I richened this up and now the car fires up and drops immediately into a nice, steady, and clean idle. Just for kicks, I pulled nearly all the start up fuel out and it acted like the throttle was stuck at 2500rpm. Timing also has an effect. Not sure how much of this applies to your code because I havent touched it, but I'm sure its the same ideas.

Rbob,

As long as you have the dust off the 8D hac can you explain a couple more areas?

L8628: Coef rpm/12.5 filter
L862F: msec startup delay
L8631: rpm iac cmd spd opn lp offset
L8699: iac min motor keep alive learning
thru
L86A0:

Appreciate your help.

Regards,
Gary Anderson

Rbob....

believew i found my problem..........was as u stated that the "steps" got stacked between the tables as u add to one it affects the others and vice /versa....

Working on a revised bin to try some real time romulating with to verify results and should hopefully have some answers by this weekend, will keep u posted

thanks
Jeremy

Not dead yet............currently have some testing on Idle SPeed Timeout Steps vs. coolant temps in process. Long as it works i will post results when have hard data confirmed
Later
Jeremy