Terrible idle surge on Speed Density

[radcon15]

Hey all, this is the first time I'm posting on the forum but I've been playing around with HP Tuners for a while. I've searched up on this topic a good amount and I've found some tips that have helped... but I'm far from figuring this out.

I've been battling this terrible idle surge on my cammed '04 LS1 GTO. Cam is a 227/235 SNS Stage 2 with stock 241s, stock ls6 intake, and longtubes. I've been using the enhanced 1 bar Speed Density OS and I've gotten it to the point that the car drives great with great throttle response, good fuel economy, fair A/F ratios throughout the rev range (although still running very rich at WOT, low 11s on the wideband while I've been aiming for 12.8), but it idles like complete crap. It used to be so bad that it would jump by 800 rpm and continue surging until it couldn't catch itself anymore and stalls out. I've gotten it to stop stalling out by almost getting rid of my Overspeed spark correction. At this point, I'm lost as to what to try from here. I've tried increasing and decreasing my base idle airflow with no real progress. Could it be too much timing in my base spark table? I haven't had the chance to try it with lower values.

And even though its not the primary concern right now.. why can't I get my WOT A/F to lean out? I feel like my PE EQ ratio is already set way lean and didn't want to continue bringing it down.

I've attached a copy of my tune file if anyone wants to take a look.
Thanks, still in the process of learning all this stuff.

Conrad GTO Tune file 15 SPEED DENSITY.hpt

[radcon15]

Oh, forgot to mention when I first start it up (doesn't matter if its a warm or cold start), it'll run extremely lean for the first 10 seconds or so and runs very rough until it finally richens up. Sorry for the mess of a tune... at least it drives well.

[cesar]

Oh, forgot to mention when I first start it up (doesn't matter if its a warm or cold start), it'll run extremely lean for the first 10 seconds or so and runs very rough until it finally richens up. Sorry for the mess of a tune... at least it drives well.

attached a picture of what i suggest to change. First, make your park and drive ignition tables match, i suggest using the drive values on both, then subtracting 4 degrees from the entire table. Then use the values in the idle overspark and underspark rpm error. Then most importantly go to your idle table and increase your base running airflow which is the bottom right table I have on the picture on the bottom right, try to get the values pretty close, especially on the ECT values you constantly see when driving. Finally, on the left are some corrections that I have seen fit with that particular cam which is lowering the rpm err time to 1 sec, the proportional to 35, and the integral to 15 rpm. I would lower the adaptive idle to maybe something lower if you have something like a cooler thermostat or fans being constantly on to keep the engine cooler. And I'm not sure what your elevation is, but the timing seems a bit on the high side. Then again, if you live in high altitude area this could be okay.

This is just to guide you in the right direction, and from my previous experiences. There are a lot of people that tend to disagree with other's tuning methods.

P.S. fix your Power enrichment table, and lower your RPM value to something like 1000rpm or so. Start with a PE value of 1.16, and adjust your VE table accordingly.

P.S. also set your p0101,p0102.p0103 code to MIL on first error, i suspect that your car doesn't fully go into speed density until it recognizes the MAF is disabled and hence runs lean.

[SultanHassanMasTuning]

use this Conrad GTO Tune file 15 SPEED DENSITY_MAS_v1.hpt

[radcon15]

Alright, I tried Cesar's suggestions and they seemed to help the rough startup/cold idle a bit, but I still have a good amount of surge going on. Also, now when I put the car in drive it wants to idle really high (1200ish) rpms. I tried lowering the airflow/spark a little while using RTT but it didn't seem to make too much of a difference. It doesn't surge right from startup anymore though, only once I give it a rev or drive it around. It settles down and stops surging in neutral/park but when I'm in gear it just wants to make the car do squats when I'm on the brake.

When I tried Sultan's tune, it did seem to make the surge tamer.. and it didn't want to surge as much when coming to a stop, but if I give it a rev or idle too long it'll start again.

I'm lost with this thing. Here's what I ended up with. I lowered the Idle over/underspeed tables again because it would stall out occasionally under Cesar's table suggestion.
Conrad GTO Tune file 17 SPEED DENSITY_MAS_v1.hpt

Thanks for helping out.

[jimmyblue]

Just what do you know, or think you know, about air mass
accuracy at low RPMs? Number one cause of idle low
frequency instability, in my book, is rich mixture. Primary
cause of that on cammed vehicles is a poor fit in the 400
and 800RPM VE table colums (made worse by cam effects,
both direct and indirect).

Directly, big cam lowers pumping efficiency and how much
of in-taken air remains in the cylinder rather than shooting
through to the exhaust (and vice versa). The balance there
doesn't have a good way to measure. Low end of VE table
loses accuracy, big time, and ends up over-predicting air
mass and overfueling as a result.

Indirectly, that shot-through intake air (plus fuel) in the
exhaust jacks your wideband reading and if you follow it
(bent lean by that air, the reading) you will push the VE
table the wrong way, even further.

Try using bidirectional controls, lock IAC and spark, play
with commanded AFR while you watch MAP and idle RPM.
You're looking for the happy place, minimum MAP to idle
where you want to be. As you improve -actual- mixture
your idle RPM will rise and MAP, drop. Keep RPM in the
ballpark by bumping IAC occasionally. When you have
found the lowest idle MAP, look at what your wideband
calls the mixture. That's going to be stoich in the hole,
"whatever" in the pipe.

Now mess with the VE table with controls released
(maybe keep spark locked) until you get the same WB
indicated AFR. How's idle stability now? At this point,
maybe play some with idle spark (bearing in mind you
need to leave some on the table, for adaptive spark
to have a free hand - adaptive spark should be off for
tuning, so you can see and fix things without it in the
mix, but turn it on in the end for drivability across
weather and aging.

[SultanHassanMasTuning]

post a log with your current tune, everything can be worked outConrad GTO Tune file 15 SPEED DENSITY_MAS_v2.hpt

you had way too much timing at idle try attached

[radcon15]

'll play around with the vcm controls tonight and try to get things settled down. I know when I play with the IAC steps a little I can get it to calm down. No matter what I try though the surge on startup is terrible, doesn't matter if its cold or hot. Cold starts are hard to keep running for the first minute or so though. What I'm still trying to figure out is why the idle wants to climb so high once I put it in gear. I matched the "in drive" and "in park" timing tables, and even tried matching the airflow with no effect on the RPM climb. When I get off work today I'll go through the routine that JimmyBlue suggested. For a log, would it be better to take a startup log and just let it idle, or to drive around a bit? Once I get it moving and drive a bit, I can come to a stop with barely any surge until it starts acting up again.

[radcon15]

got a chance to flash Sultan's modified file, and take two quick logs. First one is a cold start to demonstrate the lean condition on startup, and to show it eventually stalls out if I don't give throttle input. Second one is after I got it to idle decent, and a quick rev at the end that stalled it out. I'll be able to do more testing in a few hours.
Start and Stall 1.hpl
Smooth Idle and stall.hpl

[radcon15]

Just got a chance to mess with it some more and by locking my timing at 20 degrees, and the iac at 95 steps, I was able to get it to idle well enough to fix my VE table. Looks like I was a little lean in the 400-1000 rpm range. I also had to add a little bit of base timing again. It really doesn't seem to like 18 degrees at 800-1000, starts getting rough. 19-20 and it smooths out. It can start decent now without stalling out (still runs lean, I tried changing enrichment values and adding to the enrichment vs IAT table, no real improvement. But it does definitely feel improved.
Here's where I got to with the tune.
Conrad GTO Tune file 19 SPEED DENSITY_MAS_v2.hpt