Idle surge I can't get to go away

[Hotwire]

Hoping someone can help.

Car will idle all day long in some instances, then other times when I'm coming to a stop it starts surging, have had it cut off on me several times, but once I come to a complete stop it'll stop and idle all day long. I can save it by blipping the throttle, but can't understand what mode it's going into to cause this? I'm stumped!

2005 ECM out of a Suburban
2003 LQ4, stock internals
33lbhr flex fuel injectors
LS6 intake with returnless fuel rails, vette regulator/filter
stock truck DBW throttlebody, have brake and clutch switches installed and wired
Elgin E1839P cam (220/224, .575" lift, 112 LSA, PAC 1218 springs)
Large longtube headers
T56
3.73s
AEM wideband on a/c port

Please look over the log and tune, if you see anything that can be improved upon, I'm open to criticism! If you look at the end of the log you can see I can repeatedly get the car to go into this surging mode when coasting down my side road into my driveway.

If any other data or specs are needed, please let me know and thank you in advance!

28-Salty-tune27-reducedpetps_uppedVE.hpt5-1-21-tractorsupplytohome-tune28.hplsalty4.Channels.xml

[Matt Vardaman]

I believe it's timing related. Did you tune this pcm? The timing is very choppy and rough on the 3d graph. Hptuners doesn't recommend changing the MBT becasue it's theoretical spark advance that makes the most torque. The graph looks like someone took a sheet of paper and crumpled it up. When looking at the log I put the cursor in the peak, then valley, then peak, the fueling is swinging wildly, but the timing number stays the same. Target idle is maintained mainly by spark advance, and Iac/etc blade.

I would change the MBT table back to stock and leave it that way. Make your main spark idle cells 400,600, 800 the same number, there's some strange variance there. I know you have a manual trans, but take a look at the park/gear idle base spark tables. Put them back to a stock 01-03 Silverado, and only adjust the idle cells to make them the same. I hope that makes sense.

[Matt Vardaman]

6-18-21 Silverado PE high octane table 2.hpt Here's a copy of one of my trucks tunes if you want to use it for a compare file. It never hurts to have a sanity check on your idle tuning.

[Hotwire]

Thank you very much for the input and tune to compare. I did the tuning myself, don't be afraid to hurt my feelings, will be the first to say I don't know what I'm doing and welcome all the help I can get.

I'll work on your suggestions and report back when possible. Setup is in a 64 Chevelle, will have to wait for it to dry up around here before I can take it out and work on datalogging.

[Matt Vardaman]

Right on man. The chevelle with ls swap and 6 speed is awesome. When you get it lined out, you'll love it.

[Hotwire]

Right on man. The chevelle with ls swap and 6 speed is awesome. When you get it lined out, you'll love it.

Thank you sir, purchased it almost 4 years and am continually throwing parts at it to make it better in every way. Only thing I can't do is remove the rear doors. . Came with 305/powerglide/3.08s, 6.0/T56 is a lot more fun.

https://flic.kr/p/2kPTQs3

https://youtu.be/fU9QXOG1E4A