Hot Idle instability

[trapvette]

2008 corvette 6.2 BTR Stg3 LS3 NA cam 229/244 .630"/.615" 113+4 12cc dished 4.075 pistons 6MT

I've got my idle pretty well dialed in using BigMike42's method. MAF/VVE has a few areas that could use some minor tweaks, but I don't have much faith in my scanner setup and will likely end up chasing my tail again. something weird is causing it to show 30+% error during decel, probably some throttle transient throwing off my numbers.

1) idle and parking lot cruising doesn't fare well to high IATs due to sitting for ~10 mins. works fine if I'm just pulling in, i can ride the clutch with 0 throttle no problem. Should I mess with my IAT base spark modifier, or is there somewhere else I should be looking? I've since added 1 g/s of min idle airflow in the 1200 and 1600 rpm areas.

2) still getting a little stumbling at low throttle areas, nothing nearly as bad as it used to be. it looks like MAF could use an extra 4% or so in those areas, but I don't trust my scanner's readings below 3500hz. same story with the 1000rpm 60kpa area on the VVE. I finally got my idle where I want it and don't need to go messing it up with possible bad scanner data


VVE CL (([2320.71]+([2320.71]*([50116.156]+[50114.156])/100))-[2311.71])/[2311.71]*100
Filter [2517.161.avg(1500)]=0 and [2517.161.avg(-200)]=0 and (abs([50090.156.slope(250)])+abs([50090.156.slope(-250)]))<2 and [6310.avg(250)]=9
MAF CL (([2320.71]+([2320.71]*([50116.156]+[50114.156])/100))-[50040.71])/[50040.71]*100
Filter (([50041.223]*(273.15+[50011.241]) * (1000/[50030.91]))

[Cringer]

No one should be using Big Mike's idle guide. It causes problems like this.

[edcmat-l1]

idle trough.jpg

LOL Don't know who "Big Mike" is I'm too old to keep up with who the cool kids are these days LOL

First issue here is you've created a trough in the VVE where it idles. So if the idle bobbles some and it dips, it adds fuel making it choke which makes the bobble worse. The 600 and 400 columns should be lower than the 800 column.

Second thing is the minimum spark tables. You need to put those back to stock. Also the BRAF ect. multiplier.

You have too much idle timing in it. I'd run about 18 degrees. Put the idle and coastdown tables back to stock and just make the idle area of the table 18 and ramp it into the rest of the table.

[Cringer]

VVE CL (([2320.71]+([2320.71]*([50116.156]+[50114.156])/100))-[2311.71])/[2311.71]*100
Filter [2517.161.avg(1500)]=0 and [2517.161.avg(-200)]=0 and (abs([50090.156.slope(250)])+abs([50090.156.slope(-250)]))<2 and [6310.avg(250)]=9

MAF CL (([2320.71]+([2320.71]*([50116.156]+[50114.156])/100))-[50040.71])/[50040.71]*100
Filter (([50041.223]*(273.15+[50011.241]) * (1000/[50030.91]))

You are filtering on PIDs you are not logging. Add them to the scanner and re-log. Additionally I would suggest using these filters.

CL
[2517.161.avg(1500)]=0 and [2517.161.avg(-200)]=0 and (abs([50090.156.slope(1500)])+abs([50090.156.slope(-500)]))<2 and [50118.238] = 1.00 and [50091.156]>1

PE
[2517.161.avg(1500)]=0 and [2517.161.avg(-200)]=0 and (abs([50090.156.slope(250)])+abs([50090.156.slope(-250)]))<2 and [50118.238.avg(250)] < 1.00


1. What exactly is the problem? is idle surging at when IAT's are hot?
2. Low RPM tip in stuff will be due to VVE not MAF.

Rich on decel is pretty common and that is often times caused by removing rear O2 sensors and/or removing the cats. The ECM is looking for a heartbeat from the combination of rear O2s and cats. Just turning off the rear O2 DTC codes does not change this.

Try this tune, it should help.
post idle tuning - cringer.hpt

[Cringer]

idle trough.jpg

LOL Don't know who "Big Mike" is I'm too old to keep up with who the cool kids are these days LOL

First issue here is you've created a trough in the VVE where it idles. So if the idle bobbles some and it dips, it adds fuel making it choke which makes the bobble worse. The 600 and 400 columns should be lower than the 800 column.

Second thing is the minimum spark tables. You need to put those back to stock. Also the BRAF ect. multiplier.

You have too much idle timing in it. I'd run about 18 degrees. Put the idle and coastdown tables back to stock and just make the idle area of the table 18 and ramp it into the rest of the table.

This is the one in question. It causes people to pump up the Min Final Airflow too high.
https://forum.hptuners.com/showthrea...ght=idle+guide

[Alvin]

This car will do much better in SD, no maf.

either way the MAF should be failed and you should tune VVE by itself. I'm not a fan of using the MAF to back out VVE especially for new tuners.

[trapvette]

Thanks for all the info everyone. Cringer, here is a short log running your tune. I do have a half hour long log of the post idle tune file, but its about 9MB and won't upload normally. https://drive.google.com/file/d/1iRH...usp=drive_link

The issue with my hot idle is mainly needing to keep the revs up to stop it from stalling when heat soaked.
I've since added the missing PIDs

[edcmat-l1]

The minimum spark table needs to be put back to stock. There should never be any reason to modify that table is everything else is right. Modifying that table keeps the PCM from doing what it wants to do, because whoever is changing that table, doesn't know how to make it work correctly, without changing that table.

Hope that makes sense.

[trapvette]

Here is a log with a heat soaked start. seems to still have a few issues dropping too far below idle. I have thought about going to speed density quite a bit.

My old tuner had my idle spark at 27 and my minimum idle airflow at 13.4, so at least I got it close! i did try running 18 degrees at idle a few times. I'll get the minimum spark table back to factory settings per the repository tune i have