Anyone play with the throttle cracker settings?

[SloppyRob]

I have some really low rpm in gear idle problems im trying to eliminate and think I need to play with this table. Im trying to eliminate the surge that occurs when coming to a fast stop or when braking and turning at low speeds (parking lots etc). I looked at the tables briefly last night and noticed that the low rpm values where 0 or close to it. Im gonna try bumbing these up a bit and see if it helps out. It should as my problem stems from reversion with my cam. I just need some more air!

[jimmyblue]

I think most people fix the surging with the low-RPM VE
settings. That's what represents reversion / low suction
most directly to the fueling calcs.

I have to play with that myself, just some mild surge
with the converter and no cam / headers.

[SloppyRob]

Well, I have a question. I thought the VE tables were primarily used for cold start/ open loop mode? I have these problems once the car is in closed loop/warmed up mostly.
If i do edit these I would be reducing them, correct? (ie mult by .50) I believe i already scaled 400 x .60, 800 X .80 and 1200 by .90. following NOGO's instructions on ls1tuning.com

P.s. I tried changing the low mph values in the Throttle follower tables to 1.0 but it didn't seem to do anything....

[jimmyblue]

That's what I was talking about; supposedly that is the
"magic numbers". Though I suspect there is a fine-
tuned perfection for each motor and going too far may
be as bad as not going at all.

I think the real problem is that with a lightweight
converter you can change the natural response time of
the engine, to be faster than the IAC loop was set up
for, which changes "who's the boss" and makes it
somewhat unstable. But no way to change that, so the
key is to make the motor less twitchy.

I know this thing comes up on LS1Tech all the time but
it always looked like voodoo tuning to me, people have
just found something that "kinda works".

I wonder if maybe you want to play with the idle spark
timing, maybe a little less in the under-1000 range
would make the motor less jumpy? Though I have seen
people recommend more advance, that seems like it
would make more quick to track air. Also, check the
IAC position and be sure it's kind of centered, if it is
"hitting the stops" at one end or the other, that would
really contribute to an idle surge?

Man, you are all over this stuff... keep plowing the road.

[SloppyRob]

Yeah, i added 2 degrees for the high octane table low rpms following the idle tuning guidlines. I may try and pull that back out and see how the car likes that.

My IAC count is around 65-80 when this is happening so it's not "at the stops".

I'll try the timing first, see if it helps and try scaling the VE table a bit more. As of now i have this beast idling pretty damn good at 800rpm! Im just too much of a perfectionist to let this be good enough.

Looks like you and I both are running this tool through the motions!

Thanks for the help

[SloppyRob]

Well last night I tried a bunch of different techniques but could really do anything about this issue. I finally reverted the tune back to where I started at the beginning of the night. I tried increasing and decreasing timing under 1k, Scaling VE by 10% more, Changing low rpm throttle cracker settings, changing low rpm IAC vs. ECT, Changing Decay. No matter what I did the issue was still there so I realized I'll either live with it or bump the idle up a bit (50 rpm). As of now my idle sits at 800 (fluxuates from 790-810) with no surging problems and doesn't surge or hunt at all unless you stop really hard or creep very slowly on/off the clutch while turning. Im moving on to tuning my ltft's at cruise now.

[mrkrad]

what about drilling the TB hole so the iac won't have to react in such large swings?

[jimmyblue]

The idle hole provides an offset, but I think it is a
gain and lag problem in the IAC - when a little bit
of added air makes too big an increase in RPM, then
the IAC backs off and makes too big a decrease in
too little time, chasing its tail forever. If the IAC
update rate were made way slower this would kill
it probably.

Is there any param for IAC update rate, or max step
per update?

I've given serious thought to drilling and tapping
my TB for an Old Skool idle air bleed screw....

[Chris@HPTuners]

The throttle cracker opens the IAC motor based on RPM and MPH. It does nothing when the car is stationary...

I think you might have more luck looking at the Throttle Follower and the decay settings.

[SloppyRob]

Yup, I tried changing the decay settings and it didn't help much. The delay setting might do something.....but my problem is not a constant surge but more of a one time drop and raise to normal rpms.

[jimmyblue]

Yeah, if the decay can be made to give a "soft landing"
then you might stay out of the "dip" altogether, the
lower it goes the more difficulty the IAC has in making
it settle. Though that is more like "don't ring the bell"
and I'm still not sure how you'd muffle it instead.

[Chris@HPTuners]

from our user manual:

Throttle Follower
The throttle follower parameters are used to adjust decay and delay rates for the IAC motor during throttle closure to prevent stalling and make gear changing/selection easier.

Throttle Follower Airflow vs. TPS: This is the throttle follower airflow value used as the throttle is opened. It is the value that is reduced to zero by the decay parameters if the throttle is closed. It is versus TPS %.

Throttle Follower Airflow Decay vs. Speed (In Neutral): The decay value is the rate at which the IAC motor closes when the throttle is closed and the selector is in Park or Neutral. These values are subtracted from the current IAC Airflow value every 12.5 ms, hence higher numbers mean faster decay.

Throttle Follower Delay Time vs. Speed (In Neutral): This is the delay before the decay value begins to be subtracted in P/N.

Throttle Follower Airflow Decay vs. Speed (In Gear): The decay value is the rate at which the IAC motor closes when the throttle is closed and the selector is in gear. These values are subtracted from the current IAC Airflow value every 12.5 ms, hence higher numbers mean faster decay. The 4th Gear row is used for gears including and above 4th gear for M6 transmissions.

Throttle Follower Delay Time vs. Speed (In Gear): This is the delay before the decay value begins to be subtracted in gear.

[SloppyRob]

I guess i'll try changing both the Decay in neutral and the decay in gear again. Im pretty sure I changed the decay values to 1 before? I don't remember what the values look like as I don't have the tool here at work! Im pretty sure i made the low rpm values the same as the values in the high rpm cells. This would have fixed the problem wouldn't it?

Also how does having an M6 effect these settings?

[Chris@HPTuners]

low decay is slower. It works like this:

1. When the throttle is increasing or steady the IAC is opened extra by the Airflow vs TPS table multiplied by the Airflow Mult vs RPM.

2. When you close the throttle suddenly the value above is reduced by the decay amount every 12.5ms. ie. smaller numbers here mean slower decay.

[mrkrad]

can improper settings of these values cause surging on a flat surface in gear at low rpms (800-1500)?

like at 0-2% tps , i get some surging, what would you look for to see? log the iac desired/actual? then change what?

[SloppyRob]

I just edited the tables correctly...before i was increasing the decay values to 1, speeding up the closing!

As a reminder** I posted this up in bugs a few days ago but upon saving the tables for Decay the application adds .003 to the values you've changed!

Im gonna go try the tune out! I scaled by .70 for idle 0-18mph and .70 for first gear 0-14mph

[jimmyblue]

Yeah, I noticed tonight that at low road speeds the
values are very small decimal fractions. So I guess you
can really "feather" it at parked & slow roll, and maybe
get it to land soft or make the loop so slow that it gets
back to stable idle.

[SloppyRob]

well .70 didn't do too much....im gonna try scaling 0-10mph more. I still have a rpm drop when on the brakes that goes down 100-200 rpm then comes back up to like 950 then settles back at 800rpm. Grrrr.

[SloppyRob]

No matter what I did it did not really effect my problem. I once again reverted back to my earlier tune. I did try changing the decay values to zero which lets the idle hang at like 1000-900 for almost ever. I tried mult the values by .5, .3, .1 as well. They all effected the rpm decay but didn't solve the drop to 600 rpm. Also they didn't effect reverse with the wheel turning. I guess it just closes to a point where my cam just needs more blade open period. The car doesn't stall or anything so im prob just gonna leave it like this or bump the idle up 50rpm.

[jimmyblue]

I saw values as low as 0.01 (?) in my stocker tables, at
least down low. You still have a couple of decades to
play with. If the time-tick is 12.5mS like I think I read,
that means to swing down one IAC count in one
second wants 0.0125 as a value? I don't know how
many IAC counts you're up by. But I think the 0 MPH
count-by is what would affect true-parked idle stability
and maybe the 2MPH, 4MPH counts should be a kind
of geometric series so you get "kinda close" fairly quick,
and don't have super far to fall, so you can afford to fall
slow on the last step.

Maybe since it's something you can catch when warmed
up and regular, you could just work on the thing parked
and try 0.001, 0.01, 0.1, ... just on the piece that works
in park/neutral, maybe home in on the "magic number"
(if there is one) in 4-5 reflashes? Then with any luck the
other ones won't be too far off.