Idle/Idle Transition Tuning

[Rhino79]

Well first off, Thanks Black02SS (Chad) for poining me in the right direction earlier today. I have been battling rpm "hunting" problems for a while on a buddies truck now for a while, a 408 Silverado. I have been searching around a lot on here and found tons of helpful advice an tuning various things like idle timing, Learned Airflow tables, Desired Airlow, etc. and monitoring the correct pids. What Chad showed me today though took me 180 degrees from where I was goin with the tune. The truck started right up, idled great, all was well until you would start slowing down and then the surging and bucking would progressivly get worse till at a complete stop. As it turns out, all it too was a little more desired airflow and changing the Throttle cracker activate/deactivate speed and just like that its all good. Thanks again for the help and I hope my experience will be valuable to someone in the future!

[ArKay99]

Can I ask what the change to the cracker activate/deactivate speed was? I'm having simialr issues, not bad at all, but I feel I am close and just need a tweak.

[TAQuickness]

I've been tuning my cracker tables lately as well. For grins, I raised my activate speed to 20mph, and left the deactivate stock.

This enables me to compare the difference in driving characteristics with the cracker both active and inactive. In my case, and it's probably a rare case, having the cracker inactive made low speed drivability worse.

If deactivating the cracker does not help you, then you may need to identify the bucking area of your cracker table, then make small <5% changes up and/or down until you find the sweet spot. Incorrect values in the cracker table, especially at low load/rpm, can have a big effect on low speed drivability.

[Rhino79]

Can I ask what the change to the cracker activate/deactivate speed was? I'm having simialr issues, not bad at all, but I feel I am close and just need a tweak.

Well I started at 10 enable and 9 disable, then when it would disable it was fine but from 15-10 on decel it would hunt some, so I raised it to 18 enable and 17 disable.......problem solved! For me anyways!

[ArKay99]

TAQuickness, thanks, I'll try that tonight, was out of town for 2 days. Was in Houston BTW.
Rhino Thanks. That will give me a starting point.

[TAQuickness]

Let me know next time you're here.

[ArKay99]

Let me know next time you're here.
Will do.

[Loudmouth LS1]

Can I ask you guys a quick question, since I have no speedometer hooked up with my turbo 400, my throttle cracker should never kick in, correct? So i don't have to worry about touching it or the enable/disable speeds, right?

[ArKay99]

Can I ask you guys a quick question, since I have no speedometer hooked up with my turbo 400, my throttle cracker should never kick in, correct? So i don't have to worry about touching it or the enable/disable speeds, right?
I would think that is correct. I'm wondering if this might affect other tables where speed is a factor...

[Loudmouth LS1]

I would think that is correct. I'm wondering if this might affect other tables where speed is a factor...

What other tables ya thinkin about, anything important?

[SSpdDmon]

What other tables ya thinkin about, anything important?
If you hit Edit>Configure display units..., you can see all of the tables that reference MPH or KPH. Just sort the columns by clicking on the headers (Data Units, Col Units, or Row Units). Check all three and you'll see the VSS plays a role in various idle tables, DFCO, fan settings, as well as the throttle cracker and follower tables. You should figure out a way to get that VSS signal working again with the PCM.