H/C/I M6 Car with Idle Hang-Up when Coasting to a Stop (Log & Tune Attached)

[LS4 Racing]

Hi Everyone,

I'm very new to the tuning world, and have an issue to resolve on my swapped car.

Vehicle is a 2002 Camaro with an LQ4 block, LS3 heads and intake, and a Comp cam with the following specs: Duration: 223, 231; Lift: 610, 617; LCA 112. The shop that did the upgrades got the tuning dialed in for part-throttle and WOT, and the car runs like an animal. The only issue remaining is that when the car is warmed up and I'm coasting up to, and stopping, the idle will go up to 1800-2000 RPMs and will stay there for several seconds after I've stopped. It was even worse before this weekend, and my tuner took a swing at it to get it down to where I have described above. Since my tuner is very far away and very busy, I don't want to keep bothering him with this, so I'd like to try to solve it myself.

Attached is a log, as well as the current tune. I made some adjustments to the throttle cracker table, changing all values to 2.2 in the 0-1600 RPM range, and that seemed to slightly shorten the wait time for the idle to drop down to around 975 RPM. This was versus the previous values of 1.1 in those cells.

Before I start messing around with anything else, I really wanted to get some input, so any help would be greatly appreciated.

[LS4 Racing]

Anyone?

[THE CHAD]

had a look at your tune mate, try changing your THROTTLE FOLLOWER DELAY TIME VS SPEED (in gear) maybe try that or THE R.A.F seems a little high when ''WARM'' if that is too high it can also cause IDLE HANGING....Have you dialed the R.A.F in if not try using R Kemp idle airflow.cfg ......Cheers Bret Ultimate Lsx Tuning

[LS4 Racing]

Thank you for taking a look at this.

I was told to increase the RAF when warm, and the problem didn't resolve. Did I go the wrong way? I've attached the latest tune.

[LS4 Racing]

On the advice of another tuner last night, I disabled the Cracker completely and the problem is completely gone. I am noticing a few, very subtle drivability issues like some minor surging at low speeds, and it drops into open-loop on decel very easily, but when i put the clutch in, the idle soft lands at just around 1000-1100 or so every time, before settling in at about 950-975.

[JamesLinder]

Find out what the rolling idle RPM was set to in your stock file. I see that you now have no values in those cells. This may
be because you have a manual transmission; I only know that an automatic will have something like 750 RPM stock setting.
Your throttle following multiplier table has higher values in it than stock from zero through 3200 RPM. I would put these back
to stock settings and also put your throttle cracker back to stock settings. If everything else is tuned properly (especially MAF
and VE's) then stock cracker and follower values will work well in most cases. It appears that the throttle follower air itself
has been reduced; try this back at the stock settings too or else fixing the multiplier may result in lower air than you need.
You should zero out the throttle follower delay in gear settings for a performance car. You want the throttle follower air to
begin decaying as soon as you let off the pedal. Looking at your MAF and VE curves I would say your tuner did not do a very
good job on these. Did he install a wide band oxygen sensor in your exhaust and tune lambda error to zero to tune your MAF
and VE tables? If not then you did not get a "real" tune.

[JamesLinder]

Other than the poor tune, as indicated by MAF and VE curves, your throttle follower multiplier table from 3200 RPM down to zero RPM is
what is causing the fast idle when you come to a stop. Now that you have done away with throttle cracker air below 6 MPH, you will
have driveability issues when you open up the throttle to take off from being stopped because you are short on air. The cracker gives
extra air when you go from closed throttle to open suddenly, and the follower gives extra air when you close the throttle so the vehicle
does not fall on its face from a sudden, drastic reduction in air flow. If you post your most recent tune and the stock tune file I will take
a look and suggest some settings to improve your drivability.

[LS4 Racing]

Thanks for taking a look at this, James.

The tune was actually done at a reputable shop on a dyno with a wide band.

Attached are the current tune with the Cracker Disabled, as well as a stock 2002 M6 Z28 tune. This is one is not from my car, as the car didn't have a stock tune when I bought it.

Thanks again!

[THE CHAD]

LS4 Racing, mate if you zero out your throttle cracker table just make sure your r.a.f is spot on and I mean spot on dude........what type are those injectors.......I would put those TF/TC tables back to stock and go from there....Sorry JamesLinder I disagree with zeroing out your throttle follower delay (gear) I would zero out the table but only to 2mph and leave the 0/2mph at 1.0 sec .....but mate every tuner is different and so is every cam/engine etc.......the VE map seems a little lean/rich is certain areas......still got a maf?.....OPEN LOOP EQ RATIO I think needs attention......c.o.t disabled no cats?......lean cruise mods (mph)(sec)?.....LTFT min temp bring that down to say 104(f)... DFCO fuel cutoff enable temp -22(F)?......149(F) better......That's a quick look dude but hope you get your combo sorted out mate....Cheers Bret Ultimate Lsx Tuning

[JamesLinder]

Does it start up cold without any surging? Does it require you to use the gas pedal at all while it cold starts?
I'm trying to determine if your idle VEs are really dialed in; they look a little high.

[LS4 Racing]

LS4 Racing, mate if you zero out your throttle cracker table just make sure your r.a.f is spot on and I mean spot on dude........what type are those injectors.......I would put those TF/TC tables back to stock and go from there....Sorry JamesLinder I disagree with zeroing out your throttle follower delay (gear) I would zero out the table but only to 2mph and leave the 0/2mph at 1.0 sec .....but mate every tuner is different and so is every cam/engine etc.......the VE map seems a little lean/rich is certain areas......still got a maf?.....OPEN LOOP EQ RATIO I think needs attention......c.o.t disabled no cats?......lean cruise mods (mph)(sec)?.....LTFT min temp bring that down to say 104(f)... DFCO fuel cutoff enable temp -22(F)?......149(F) better......That's a quick look dude but hope you get your combo sorted out mate....Cheers Bret Ultimate Lsx Tuning

Injectors are 42 lb'ers. Exhaust is long-tube headers into true duals with no cats. Not sure why he set DFCO as such.

Does it start up cold without any surging? Does it require you to use the gas pedal at all while it cold starts?
I'm trying to determine if your idle VEs are really dialed in; they look a little high.

Starts up cold with no issues. I don't need to use the pedal at any time. After reading yours and Bret's comments about RAF, I was going to run the RussK config to see if I can get that nailed down. As mentioned before, the only issue I've noticed since disabling the cracker is some very light bucking/surging at lower speeds and in high gears, say like 45 MPH in 5th gear.