I've had an idle problem ever since I put in this stinking LUK aluminum flywheel (regret). Lets just say the cam and the flywheel don't mix, I installed the cam first and then I put the flywheel in about 5k miles later. I've had problems with my idle for 4 years now...
Anyway I'm trying to make my idle not drop like a rock when I push in the clutch, this seems to be one of the main problems because it drops so fast that it falls all the way to ~500rpm and then the dreadful surging starts (quick & cyclic between 500-1300 rpms). VERY important piece: Idle problems are ONLY when I'm coasting, as SOON as the car comes to a stop the idle fixes itself within a few seconds at most, sometimes instantly. My car has been professionally tuned twice, the second time most of my idle problems went away because I voiced this as one of my main concerns. The second tuner also fixed another horrific problem, stalling and worse surging with the a/c turned on. Even with the second tune once in a while my idle problems randomly re-surface and that is what I'm trying to eradicate.
I've modified the throttle follower, throttle cracker, idle airflow tables, etc. countless times and nothing seems to work or even have much of an effect, unless I change it a ridiculous amount. If a setting doesn't work I change it back to how it was and start from scratch. I also have tried changing settings under "torque management" because I was told those settings are where I need to compensate for the reduced weight of my flywheel (10lbs vs 24lbs stock), I didn't notice any changes in the engine's behavior when I modified this settings, no matter how extreme.
If all else fails I'm going back to a standard flywheel because my idle was fine even with the first tune before it I installed it.
I've fought many of them. Some of them, the return to idle (TF,TC) tables seem to work right, others don't. The ones that don't, like yours, I've had to drastically increase the RAF table, until it causes the idle to hang, and then systematically work it down until it hangs about 50-100 rpms above idle til you come to a stop.
One of these days I'm going to try swapping a PCM in one that's not working right, and see if it's not a internal PCM problem.
I have struggled with the same issue on my 2004. Interestingly, I have found the throttle cracker deactivates when you depress the clutch and when you release the gas the TF will decay per your tune. So during this cruise down to 0 mph the rpms will drop and sag below 500, sometimes stalling.
I have managed to improve the situation by logging the car during these situations and actual utilizing the timing values in the Main Spark Advance table and corresponding RPM/Cylinder Airmass cells (will be low because of no load) as a means to keep the rev's up (similar to the over/under idle timing approach) unitl you reach 0 mph and the Adaptive Idle circuit takes over (Under/Over speed timing). Just another idea that may work when combined with all the other suggestions to help add the finishing touch........
This is my experience, but of course I have a paying day job and tuning is more a hobby so your mileage may differ.....
I've fought many of them. Some of them, the return to idle (TF,TC) tables seem to work right, others don't. The ones that don't, like yours, I've had to drastically increase the RAF table, until it causes the idle to hang, and then systematically work it down until it hangs about 50-100 rpms above idle til you come to a stop.
One of these days I'm going to try swapping a PCM in one that's not working right, and see if it's not a internal PCM problem.
A bad PCM would explain a lot, you saying that made me remember a bad OBD I PCM I had long time ago in an '86 z28 TPI. 98% of the time it would run normally, the other 2% the idle would be erratic and I would get MAF codes. I ended up replacing the PCM and that fixed it.
Odd that my problems are similar, it seems like an unlikely scenario to have this happen again and on an OBD II. I would be very interested to see what happens when you swap out PCM's.
Can you give us your cam specs ??? With a cam swap as i assume you did you can add timing to the "base timing in gear" table-this helps with dying--typically you can fix your issue with the cracker/follower/desired airflow tables--but sometimes you must do more----I would also make sure ALL your DFCO (deceleration fuel cutoff) settings are turned OFF--usually on a M6 they are
I'm sure you have but check for vacuum leaks or air intake/filter leaks
What are yout fuel trims like ??? Do you have larger injectors ???
Can you give us your cam specs ??? With a cam swap as i assume you did you can add timing to the "base timing in gear" table-this helps with dying--typically you can fix your issue with the cracker/follower/desired airflow tables--but sometimes you must do more----I would also make sure ALL your DFCO (deceleration fuel cutoff) settings are turned OFF--usually on a M6 they are
I'm sure you have but check for vacuum leaks or air intake/filter leaks
What are yout fuel trims like ??? Do you have larger injectors ???
X-ER 224/228, .581/.588, 114 LSA
DFCO- off
Fuel trims I had the LTFT's dialed in fairly well before my second dyno tune. After the tune the LTFT's went south, usually -10's. The car runs much better now than it did when I had the LTFT's dialed in. The fuel economy is slightly better now too.
My stock file (98 6 speed) has the enable temp @165 .
I used Russ Kemps Idle airflow config to tune the base running airflow and added some timing in the underspeed table while also adding to the lowest cells of the craker table.
I beleive on a M6 the DFCO is turned off anyway---On some larger cammed motors with an A4--the DFCO does not operate correctly and will make it dye when coming to a stop --you can try and dial it in to make it work but it is difficult--The reson for the fuel cut-off is for mileage--but most people with cams care little about mileage and care more about driveability issues like stalling
Huttler--did you try and disable the fuel trims ??? this helps on larger cams--Also--find what the MAP KPA reading is when coming to a stop when it dyes--A stock cam has a very low MAP reading at idle/low RPM's around 15-25 KPA--But with cams I've seen the idle MAP in the 50-60 range--So for example if you are idlieng at 60 KPA instead of 25--it may help to adjust the IFR table in the 60 KPA range somewhat larger (will make the pulse shorter) Larger injectors always seem to make the idle/stalling problems occur-- Remember that in the IFR table the scale is shown as the recipricol of 100 KPA-(60 KPA is 40 on the IFR table)
ALSO sometimes it helps to set the PE MAP threshold from the stock 15 KPA (EFILIVE table B3613) to something higher than your now higher idle KPA--like maybe 65 KPA
My stock file (98 6 speed) has the enable temp @165 .
I used Russ Kemps Idle airflow config to tune the base running airflow and added some timing in the underspeed table while also adding to the lowest cells of the craker table.
This completely fixed my stalling issue.
Both tuners recommended it be off, I'm not sure why this is. I have re-enabled it before and it doesn't seem to affect anything
One of the primary enablers of the DFCO system is engine MAP--
With a stock cam typically at idle the MAP KPA is in he 25 KPA range and goes up with engine load--However with an aftermarket cam often the idle KPA is like 60 --- BUT with a small/medium load underway it immediately goes down to the 25 KPA range and them starts to move up the KPA scale with increased load-- It gives the ECM mis-information and the it thinks that is it is underway with a load at idle --But shortly after a small load when underway when the KPA goes down momentarily---If you lift off the throttle it will try to kill the motor by cutting off the fuel-- It also may go into a cycle of surging as the KPA bounces up and down until you come to a complete stop---Another enabler/disabler is MPH--That's why when not moving the DFCO won't trigger--Confused ?? All this stuff happens very quickly and just for milliseconds--but it is enough to make it want to dye or surge--
So for example if you are idlieng at 60 KPA instead of 25--it may help to adjust the IFR table in the 60 KPA range somewhat larger (will make the pulse shorter)
That's a hack way of doing things and I would never recommend altering the IFR table to try and cure a stalling problem. The IFR table is one of the 2 basis' that the entire calibration is based on. Changing it will change everything fuel related in the corresponding vacuum areas. The IFR should be properly set, along with the displacement, and everything else should work off that.
If a stalling problem cannot be cured using conventional methods, I would sooner recommend altering the base airflow table to help.
If you read his original post--he has already tried adjusting the 'desired airflow" table with little or no results--so I am just suggesting other tables that might help with his problem---It is not a hack way to fix things--especially sinse he has installed larger injectors and the problem might be in the IFR scaling table---tuning 101 detates if you change the air intake or the way the MAF sees the air--work on the MAF table---If you change the injectors--work on the IFR table--Being that he has tried all the usual tables to correct dying/surging--it is very possible that the IFR table is not scaled correctly--Quite often when you buy aftermarket larger injectors they flow differently that what it says on paper---it is a very likely progression that sinse he has tried everything else that the IFR table is askew----working on the IFR table when it is in closed loop will only help the part throttle fueling--His problem is NOT at WOT but rather on deceleration or lo RPM's - having -10 LTFT's- with the new injectors only proves that an adjustment in this table is warranted--You never agree with anything i reccomend mostly because you are a LS1tech advocate---As recent developements show--LS1tech has gone in the Crapper---mostly because of people like you---You critize without reading thoroughly when all most are trying to do is make suggestions for posters to try and solve problems---you assume that all C5 owners are idiots--But the poster has said he has tried everything and is looking for other suggestions---My suggestions HAVE worked to solve similar issues--I don't kow what your agenda is but being that you are a LS1tech advocate--I'm sure you have a hidden one---
One of the primary enablers of the DFCO system is engine MAP--
With a stock cam typically at idle the MAP KPA is in he 25 KPA range and goes up with engine load--However with an aftermarket cam often the idle KPA is like 60 --- BUT with a small/medium load underway it immediately goes down to the 25 KPA range and them starts to move up the KPA scale with increased load-- It gives the ECM mis-information and the it thinks that is it is underway with a load at idle --But shortly after a small load when underway when the KPA goes down momentarily---If you lift off the throttle it will try to kill the motor by cutting off the fuel-- It also may go into a cycle of surging as the KPA bounces up and down until you come to a complete stop---Another enabler/disabler is MPH--That's why when not moving the DFCO won't trigger--Confused ?? All this stuff happens very quickly and just for milliseconds--but it is enough to make it want to dye or surge--
Awesome tips given, I'm chasing a bit of low speed, low load surge, Thank you.
I can relate the PE enable KPA to the Holley power valve, if the power valve vacuum opening point was near idle vacuum it would open. Of course causing mileage problems, rough running conditions etc. Now I'm going to go fix mine!
I asked the question regarding the LS2 TB because I recently had a pro email tune were the TB was rescaled the wrong way causing similar issues to OP question.
If you change the injectors--work on the IFR table--Being that he has tried all the usual tables to correct dying/surging--it is very possible that the IFR table is not scaled correctly--Quite often when you buy aftermarket larger injectors they flow differently that what it says on paper-His problem is NOT at WOT but rather on deceleration or lo RPM's - having -10 LTFT's- with the new injectors only proves that an adjustment in this table is warranted--
You didn't recommend he rescale his IFR to help fueling, you recommended he change one cell to help return to idle. That's hack.
Quote:
Originally Posted by tblu92
You never agree with anything i reccomend mostly because you are a LS1tech advocate---As recent developements show--LS1tech has gone in the Crapper---mostly because of people like you---You critize without reading thoroughly when all most are trying to do is make suggestions for posters to try and solve problems
What does LS1tech have to do with it? I'm on both boards, so are alot of people here.
Quote:
Originally Posted by tblu92
you assume that all C5 owners are idiots
That's just an idiotic thing to say. I don't think C5 owners are idiots, just you. You consistently give horrible and misleading advice. Your type is terrible too. --- instead of periods. WTF is that?
Quote:
Originally Posted by tblu92
I don't kow what your ajenda is but being that you are a LS1tech advocate--I'm sure you have a hidden one---
My agenda is to give some sound advice and try to keep people from listen to you. It has nothing to do with LS1tech. Don't know why you're involving that.
Would you like me to link the dozen or so threads where you've given some hack advice, or just flat didn't know what you were talking about? Remember the 02 sensor you didn't know was unplugged, and I diagnosed it over the internet?
I've seen you post some decent info a couple times, Those times I've left you alone. When you post crap, I'm going to call you on it.
BTW, to the OP and everyone else on here, LS1tech gave this guy the title of "minister of misinformation." Do a search on his posts over there.
I'm sure I'm an "ls1tech advocate" (whatever the hell that means) and I usually don't say a word when you post things here, but I can't keep my mouth shut for this.... Adjusting a single cell of the IFR is what people did before they realized that they could tune the VE/MAF, and is not what that table is for.
You are right; aftermarket injectors that have not been flowed have variation, but not in ONE SPOT. So that we never have to have this argument again, here is why your IFR should be a relatively straight line; here is the physics model used to derive flow in the face of differential pressure: http://en.wikipedia.org/wiki/Bernoulli%27s_principle Using this model will NEVER generate a hump or hole in the straight line that is your IFR.
I have had a few vettes that seem to ignore the TC table at clutch-in. There MUST be a trigger parameter that we do not have access to. In those cases, I use personally use spark in the HO/LO tables at dip point and higher than 'needed' idle airflow as Ed mentioned (and zero the TC table). This approach doesn't always work for big cams because it can exaggerate cam surge.
I'm back off to my lurk corner on this board, best of luck getting the car straight.
Last edited by Steve@TunedbyFrost.com; 05-18-2009 at 02:41 AM.
Corvette Store
idle problems/ idle decay
If a setting doesn't work I change it back to how it was and start from scratch. I also have tried changing settings under "torque management" because I was told those settings are where I need to compensate for the reduced weight of my flywheel (10lbs vs 24lbs stock), I didn't notice any changes in the engine's behavior when I modified this settings, no matter how extreme.
I had the LTFT's dialed in fairly well before my second dyno tune. After the tune the LTFT's went south, usually -10's. The car runs much better now than it did when I had the LTFT's dialed in. The fuel economy is slightly better now too.
