as the title says. my car idle surges bad and it is very,very irritating. every once in a blue moon i can come to a stop and it settles down to 950 like it should but most of the time it drops to around 500 and surges to 1500 or so,alot of times it does that quite a few times untill it finally finds a steady idle,sometimes it drops so low it dies .i tkink my iac count is in the 5x range at idle,should i lower to 30 or alittle less or what ? any and all suggestions apreciated
thanks,mark

 

I would try and raise your desired airflow and see if that helps the problem. It sounds like you don't have enough air.

 

use a scantool and log your idle airflow vs actual I think its desired vs actual airflow or something like that. Cylair_DMA -->airflow grams/cyl vs MAF grams/sec that will work and use the part of your scantool that graphs the lines as you record.

also watch your IAC (which is your idle air control...should be something like 50-60 steps or so at idle)... just read all of ur post... your IAC's are fine.

with your IAC count being ok i would think that you just need to adjust other tables, not your airflow or adjust your TB any..

i would say get your spark tables for in gear and in park neutral (base spark in gear and base spark in neutral) and adjust them to 22 or 23.. also adjust your high octane at those same areas to 23 also.

what i did was increase those tables to 23 from 0.08g/cyl to 024 g/cyl and up to 1200rpm all to 23... if i ever get any surging its due to the car re-learning the trims and how to run, as i would have adjusted IFR and injector stuff.

 

Once you get the desired airflow dialed in, you should use the BIDI controls to manipulate spark and AFR until you find the sweet spot that yeilds best vacuum/desired behavior.

 

Take away the effectiveness of the IAC to control idle some and let the spark correctors do more of the work. I think two big contributors to the issue is the direct airflow correction AND the low spark correction. The spark correction will add up to 9* IIRC when the idle drops 200~300RPM. But if it drops futher, the correction drops back down significantly and doesn't add as much timing in to correct the idle. This leads to the IAC taking over. Take a look at your spark correction table for lower than commanded idle speeds and make some adjustments. Then, make some adjustments to the extreme end of the IAC direct airflow corrector. The car breathes easier with the new setup. Therefore, it doesn't need as much of a correction. Scale the top end of the table for lower than commanded idle speeds down a little and see if that helps.

 

The idle spark advance table wants to be matched up to main
where they abut, and at RPM below desired in that table the
spark can be given a tapered increase to make it tend to come
back up. Corrections can do the same thing I guess, but the
idle spark table seemed way short to me (at least after I had
bumped up the main one methodically).

Look at the throttle cracker table and see if it has irregular-
looking features. If it's jagged like some I've seen it can make
more tricky the transition to idle. You want that to be really
soft and slow (in "PCM time") so the idle RPM loop is not
being challenged to keep up.

Airflow consumed, you should look at the Dynamic Airflow to
see what the PCM "thinks" is the "real" air; MAF is liable to be
not-accurate (see 2500Hz in still air, etc.) and also not the
whole airflow quantity used; a small weight at idle RPM.
The idle airflow values I used to put at 10% below what I
saw used but lately I'm thinking it's better to overshoot the
observed mark and let idle RPM trimming have to bring it
down. It may be no more stable but at least any initial
error will tend to make the engine live instead of die.

You may want to look at the NBO2 voltages with an eye
to their switching nature. If they are square and pegging
back and forth, or rectangular (spending more time pegged
one way than the other) try decreasing the proportional
fueling amount in the airflow modes near idle. Ideally the
NBO2 will have a full swing but the peaks / valleys will be
more triangular, not spending a lot of time clipped (which
is showing that your in-the-moment mixture is being over-
driven, rich and lean, which then bumps RPM and makes
the idle loop constantly stimulated). There can be O2
response time lags bothering the loop stability and any
tightening-up of the mixture perturbation/feedback is a
good thing (as long as the O2s still switch reliably).

 

I like the way you put that.

 

thanks guys.i just noticed coming back from lunch on my wideband when i parked with it in neutral the wideband was reading around 12:5-13:3 and it was surging and when it finally found idle it went back up to 14:7-15:2 or so .it seems to be rich when it is surging.

 

wondering if you fixed it yet?

 

would a dirty maf senson cause it as well? jsut curious.

 

I would 1st look for vacuum leaks anywhere on the manifold or throttle body..make sure everything is solid..

 

Do you ever get error codes for slow-switching of your 02s?

 

possibly, yes. dirty air filter/maf cause all kinds of problems, the airflow readings can get very scattered and cause wrong fueling, bad transitions, hesitation, etc.

 

That is way too rich for idle. What are the LTFT's? Reducing the lower region of the main VE and increasing the values in the Desired Airflow In Gear and P/N will go a long in helping the surging.

 

i haven't had much time to mess with yet much since it has been such bad weather lately. we cleaned the maf and it is not setting any codes. i've leaned it out some but it is still on the rich side. i didn't look at my ltfts yet to see where they are at but i'll look and see what they are.i'll also raise the desired airflow some. the main problem is if i am just setting still at an idle is when it surges from 500 up to 1500, alot of times it does that a few times and finally settles at 950.oh yeah,when it is surging the iac counts goes from 5x to 15x range.

 

Did you mess with the idle over/underspeed settings in the idle spark section? I noticed on mine that if my idle dropped 150RPM below desired, the PCM would add in 9* of timing to help bring it back in line. However with the stock settings, if it dropped more than 250RPM below desired idle, all the help from the timing disappeared.

My theory is, since the timing isn't there to help cure the 450RPM difference between your swinging idle and your desired idle, the IAC valve is working overtime. The problem with that is, it's not really fast enough to keep up with and react to idle like spark is. Find the table that "directly" adds airflow via the IAC valve to cure idle discrepencies and try taking 10~15% out of it (weakening it's influence) and then bring the spark correctors to more reasonable numbers so the spark can actually make a difference.

In EFI Live, the tables I'm talking about are:

Spark>Idle>Idle Overspeed Error
Spark>Idle>Idle Underspeed Error
Idle>Learning>Direct Airflow Correction

I don't know what they're called in HPT (if that's what you're using).


**EDIT** I just realized I wrote basically the same thing above.

 

i've got the idle overspeed taking out 9 * at 300 rpm over and going down to something like -2* at the first setting and it is also adding 9* at 300 rpms under tapering down to 2* or 3* at the first setting.
i can't remember what the idle>learning>direct airflow correction is.

 

Any updates on this? I'm having the same problems. I blame the 90/90 because the car never came close to having this much trouble with idle with the ls6 intake. I've sprayed it down for vacuum leaks but found nothing. Let me know how you guys make out and I'll post up if I find some positive results. I have my idle timing down in the low teens right now because that's the only thing that seems to help. I'm gonna play with the underspeed/overspeed tables to see if I can get it to stabilize itself.

 

Ive switched from a my stock LS1 intake to an LS6 unit and only have fuel trim issues that ,when adjusting, doesnt seem to change at all. Running at 20-25 long term even after maxing out my tuner at -5%!! I didnt change the intake gaskets during install because the intake only had 18000 original mile on it. My buddy says that he believes its got a vacuum leak!! Im pissed that evrything is painted to detail, including the intake, and now its gonna look like ***, just to find a stupid vacuum leak that I may not have!!

 

Since my last post I've had luck calming my idle. Jimmyblue made a post talking about the significance of the 400 rpm column in the VE table. My 400 rpm column was rich and making the idle mixing rich which played a factor in the surging.
The other problem I was having (going back to basics) is that I'd been making little tweaks here and there for a while and never smoothed my VE table. I had little peaks and dips all over which I'm sure was creating problems in my VE.
Once I fixed the 400 column and smoothed out my VE table the car was idling well. I was then able to bring the over/underspeed tables down close to idle speed.
The car finally idles well. Under certain conditions it'll search a little but settle itself. I could never turn on the maf before because the car wouldn't want to stay running but I can now and I've started tuning the maf. Hopefully this can help some of you guys as well. I know it was making me insane.