RPM surge while slowing down in neutral

[dantheman1540]

I've been working on a few driveability issues on and off for a while now and I sorta have it down to two things. The vehicle is a 04 Tahoe with a LQ4, 862s, 224/228 113lsa cam, 5 speed swapped, LS2TB, NNBS Intake, and runs 93 only.

First is rpm surge during deceleration while in neutral clutch in or out. For example when coming to a stop from say 45mph as soon as the clutch is in or the transmission is in neutral the RPM quickly drops down to idle around 700 and holds fine until right at 15mph where it jumps up to around 1,300 and hangs for a second before slowly dropping back down. This can be found between1:19-1:21 in the A1 log

The second is that sometimes instead of surging up at about 15mph during deceleration it stalls and shuts off. I do not have a log of this as it is rare.

Just looking for some direction on what to do next as I am kinda out of ideas and don't want to go shotgunning stuff.

Dan Mod 53 Minor idle spark reduction..hptA1 Surge.hpl

[dantheman1540]

This morning I was not logging data but it stalled 4 times coming up to a stop.

I have tuned BAF specifically starting when engine temps were cold and letting it idle up to temp with no accessories on, I found this technique somewhere on here.

I'm wondering if its something to do with the Manual trans swap. Anyone have any Ideas?

[DougO]

adjust your idle airflow not your base running airflow

[dantheman1540]

adjust your idle airflow not your base running airflow

The main table I have messed with to try and fix this issue is the "Idle Airflow" table under Engine>Idle>Airflow>Base Running Airflow. Is this the wrong table? I do not see another option for adjusting Idle Airflow but I may be missing it. Idle airflow.PNG

I have adjusted this table in increments of 2% in both directions and used the RussK Method multiple times but I still have this issue.

[Matt Vardaman]

You changed the throttle body. Take a look at throttle follower and throttle cracker tables. The Idle tuning section on this site covers how to adjust under the big cam idle tips and tricks. Just a suggestion. I think it will help your problem of Idle hang and surge. Your Base Idle airflow table is the point the iac/etc throttle come back to. BAF is the startpoint, it just needs to be set at whatever your engine needs to make the LTIT (idle trim) as close to zero as possible. Also a manual transmission might not use these tables at all and might use the Rolling idle feature, you might pull a tune file from the repository with an early model 99-00 5-speed fullsize truck.

After looking at your Tune file: high octane has 25* at idle, low octane has 28* at idle. Making these match will help sometimes. Your VE table looks look the rocky mountains, and might be the cause of stumbles and stutters during transitions. It should be smooth without any sudden dips or rises. I hope this helps you some. The compare feature is the best when you need to check your changes against other modified tunes. Also you might share your scanner config so I can view your log with your afr match, mine is different.

[Matt Vardaman]

"The second is that sometimes instead of surging up at about 15mph during deceleration it stalls and shuts off. I do not have a log of this as it is rare." The throttle cracker table is speed and rpm based, that might explain the surge at that mph.

I attached my tune file so you can see the difference between the throttle cracker tables between yours and mine. I edited mine according to the extensive idle tuning thread on the forum. Also try viewing your tables as split table/graph (3d/2d)
5-31-21 Silverado in gear idle down 10 rpm baf adj.hpt

[dantheman1540]

You changed the throttle body. Take a look at throttle follower and throttle cracker tables. The Idle tuning section on this site covers how to adjust under the big cam idle tips and tricks. Just a suggestion. I think it will help your problem of Idle hang and surge. Your Base Idle airflow table is the point the iac/etc throttle come back to. BAF is the startpoint, it just needs to be set at whatever your engine needs to make the LTIT (idle trim) as close to zero as possible. Also a manual transmission might not use these tables at all and might use the Rolling idle feature, you might pull a tune file from the repository with an early model 99-00 5-speed fullsize truck.

After looking at your Tune file: high octane has 25* at idle, low octane has 28* at idle. Making these match will help sometimes. Your VE table looks look the rocky mountains, and might be the cause of stumbles and stutters during transitions. It should be smooth without any sudden dips or rises. I hope this helps you some. The compare feature is the best when you need to check your changes against other modified tunes. Also you might share your scanner config so I can view your log with your afr match, mine is different.

Hey Matt thanks for the help! So I also own an 05 factory manual trans truck and have used that for reference on many things. With the manual swap, the truck thinks it's in D4 at all times so I know for sure nothing labeled P/N is applicable but I am fairly certain BAF is taken into consideration as large changes cause all sorts of issues but I believe using the RussK method I have that fairly dialed in.

Your totally right about the spark tables typically I have them match during turning sessions, I fixed that and they both match for the time being.

I noticed the VE table looks rocky but other than the issues discussed here I have no weird driveability problems. When I log AFR error its typically within 1% in all cells so I hate to change cells based on the appearance of the graph and not the real time data in the histogram. Maybe thats foolish of me IDK but for this version I smoothed a few areas.

The rolling idle feature never seems to make much difference, so I am not sure if it is using that table due to the manual swap. I suppose I should do an independent test of this to confirm my suspicions.

I see what you mean that our throttle cracker tables are significantly different, I actually used the table from my 05 truck and copied it to this one. The other truck used to have this exact cam in a 6.0 with a blower and never seemed to have this issue so I thought that was a good idea but I will try your table and see if it makes a difference. I need to run back through the idle thread you mentioned, I'm sure I've read through it before but its so easy to get lost in the sauce. I also noticed I had the throttle cracker enable/disable speed both the same which I have heard is a no-no so I fixed that.

I think I have a decent setup to try on my way home from work so I will report back and include my scanner config for you.


Thank you!

[Matt Vardaman]

I read that entire Idle tuning forum thread three or four times, and it can be overwhelming when you are first starting out. I adjusted my throttle cracker just recently, after reading a few posts about "cruise control feeling" after cam install. My cam is small, so the effect was mild. The adjustment definitely helped. The Ve table isn't really a big deal since it is just a reference when running a MAF sensor. I hope you get your problems lined out! A manual transmission is awesome, I wish I had one in mine.

[dantheman1540]

Made a little progress on the RPM surge by adjusting the throttle cracker airflow table lowering the values in the 1,000-1,600 rpm/12-16mph cells.

Have not made much progress on the stalling issue with adjusting the TC table so I'm gonna give it a few more small increments and hope it helps, otherwise back to the drawing board.

Here is the most recent log, tune, and scanner configs. It stalled twice before I remembered to click record

[smokeshow]

Better start by changing max idle - gear back to the stock value, around 1200rpm or so. At 850 you're just crossing that value all the time, entering and exiting idle mode. This almost always causes instability. Also smooth out / reduce the throttle cracker table - prevent more instability from sharp changes as RPM moves around. If you need more idle airflow, for a gen 3 manual in this case it will need to be added to base running airflow. Idle spark is too high, especially as it is higher than main spark. You want to soak up torque reserve to help accelerate when you go on-pedal and get into main spark, not the other way around. High load / low RPM areas when you clutch out to start moving are pretty low on spark as well...looks like the truck is soggy as you take off as a result. I'd also cut the entire throttle follower airflow decay in gear in half. The bigger the camshaft, the more sensitive it is to fast airflow/spark changes.

Start with those changes, see how it responds.

[THE CHAD]

Made a little progress on the RPM surge by adjusting the throttle cracker airflow table lowering the values in the 1,000-1,600 rpm/12-16mph cells.

Have not made much progress on the stalling issue with adjusting the TC table so I'm gonna give it a few more small increments and hope it helps, otherwise back to the drawing board.

Here is the most recent log, tune, and scanner configs. It stalled twice before I remembered to click record

.......Have you dialed in your Base Running Airflow (idle airflow), if still surging you'll need to dial that in from cold till running temp, then once you have got that close STIT within say -1.00- -1.50 as a rough amount some may need a tad more, then see how that goes, get that dialed in first mate...if anymore sometimes than say STIT of -2.00 it can cause idle hang..