Idle dips and hunts when clutch in and coming to stop

[04Vette]

Hey all, there is a ton of great information here, but it's tough sifting through it all to find the someone with the same issue I'm seeing. To start, I'm working on a 2004 Corvette Z06 (LS6). All I've done is add a TSP Torquer V2 Cam, supporting mods like springs, pushrods, trunnion upgrade, and American Racing Headers. Stock heads, stock intake, and stock injectors.

I've had some nice progress tuning the VE tables and MAF tables, but I can't seem to eliminate this issue where the idle fluctuates a lot when I am rolling to a stop with the clutch in. I've noticed that once I hit 0 MPH, it stabilizes. (Stock has a rolling idle table, but it's all zeroed out. I tried changing it to 850, but it didn't do anything for me)

Since my tables were looking pretty good, I decided to merge them and re-enable everything to see if it would fix itself. It seems like with everything re-enabled, its hit or miss whether it still does it, so there's definitely something I need to work on. I'm attaching my latest tune (isolating MAF) and its corresponding log file. You have to scrub a good amount in to approximately 04:34:12 for when I came to a stop, but you can see it dips to about 300 rpm in that case.

(This was a big hill up and over [in Mexico obviously] that I can put a nice even load on the engine and pull from fourth gear to the moon well before hitting the top).

Looking forward to hearing from some of the more experienced tuners on here...

[SiriusC1024]

Work on that VE table some more. This time re-enable CL and use STFT's.

[04Vette]

Shouldn't I be using my wideband to evaluate the VE and MAF error? That is why closed loop is disabled and so are STFT's. (Also is it really true that my STFT's were disabled during open loop from the factory?)

[SiriusC1024]

No. Wideband is for high map/rpm. The high load regions.

[Aggie3rdGen]

You're very lean on your full throttle pulls. You need to target 12.5 AFR during WOT.

To Sirius's point, you should be more lean as you get closer to idle. Can't trust your wideband as much here as you now have unburned fuel from cam overlap distorting the AFR readings.

[edcmat-l1]

Open loop tuning is the dumbest thing ever introduced to the common man. Aftermarket widebands are notoriously inaccurate and you combine them with a cam with some overlap and they can't be trusted. Unplug it and leave it unplugged until you're ready to dial in the WOT fueling. Put it back in closed loop, turn off the long term trims and plot the short terms in your histogram.

You also need to fail the maf so you can tune the VE. It is not failed in the file you posted.

[SiriusC1024]

Yes OL tuning in place of CL is bad practice. Just so people don't start the tired debate of accuracy of a wideband vs narrowband sensor itself, don't neglect to consider the most important part - the fuel trim algorithms. You don't have that with a WB. That's why I personally prefer STFT and LTFT being logged. Don't want to refute you ed, just that's what I'm comfortable with.

[edcmat-l1]

Yes OL tuning in place of CL is bad practice. Just so people don't start the tired debate of accuracy of a wideband vs narrowband sensor itself, don't neglect to consider the most important part - the fuel trim algorithms. You don't have that with a WB. That's why I personally prefer STFT and LTFT being logged. Don't want to refute you ed, just that's what I'm comfortable with.

Doesn't sound like you're refuting me. Sounds like you're agreeing with me. Perfect example of WB inaccuracy is the other thread where the OPs WB is off a full 2 points.

[Alvin]

Hey all, there is a ton of great information here, but it's tough sifting through it all to find the someone with the same issue I'm seeing. To start, I'm working on a 2004 Corvette Z06 (LS6). All I've done is add a TSP Torquer V2 Cam, supporting mods like springs, pushrods, trunnion upgrade, and American Racing Headers. Stock heads, stock intake, and stock injectors.

I've had some nice progress tuning the VE tables and MAF tables, but I can't seem to eliminate this issue where the idle fluctuates a lot when I am rolling to a stop with the clutch in. I've noticed that once I hit 0 MPH, it stabilizes. (Stock has a rolling idle table, but it's all zeroed out. I tried changing it to 850, but it didn't do anything for me)

Since my tables were looking pretty good, I decided to merge them and re-enable everything to see if it would fix itself. It seems like with everything re-enabled, its hit or miss whether it still does it, so there's definitely something I need to work on. I'm attaching my latest tune (isolating MAF) and its corresponding log file. You have to scrub a good amount in to approximately 04:34:12 for when I came to a stop, but you can see it dips to about 300 rpm in that case.

(This was a big hill up and over [in Mexico obviously] that I can put a nice even load on the engine and pull from fourth gear to the moon well before hitting the top).

Looking forward to hearing from some of the more experienced tuners on here...

With that cam you might get better results in SD mode. When you did the VE tables.. did you fail the MAF sensor first? It doesn't look like it. Having a rich or lean spot the engine passes through as it returns to idle is 99% of the time the issue. Using a wideband while dialing in the VE in driving areas will give you a more defined shape than relying on fuel trims. On GEN 4 the fuel trims are much faster to settle and can be used better to dial in VE.. In my opinion its too slow/unreliable to get the exact shape needed for a good running GEN 3 cammed car.

Don't forget to use the wide band to get areas lower than the desired idle too.. That is something that would be about impossible to do with fuel trims alone. Say if your idle is 800 RPM but it will idle at 550 but roughly.. do that so that you can dial in the fueling there. That way if the idle should happen to dip for some reason it isn't too rich/lean and dips further.

[04Vette]

I appreciate the feedback here. I have been working on my tune when I can. To answer a common question here about whether I failed the MAF or not... Yes. When I am working on VE, I fail the MAF. As I mentioned in the original post, I re-enabled them both to allow them to work together to hopefully eliminate the problem. One thing I've noticed is that when I am working on tuning my MAF, the problem is much worse. When I am working on VE, it's pretty much non existent. I'm not sure I trust some of your guy's opinion about my wideband not being accurate. My wideband reading on VCM scanner matches my gauge readout...

But since I am open to trying new things, I am going to go out and do some tuning making corrections based off STFT's.

Here is my latest tune and its previous log using STFT's...
VE Tuning13 and MAF Step 12 changed stoich back to 14.7 throttle cracker put back to stock.hpt
VE12 Stoich at 14.7.hpl

I had my stoich afr set at 14.2 because I am in Cali runnning 91 octane, but I quickly observed that the O2 sensors have a calibration that is probably determining rich/lean based on the original tune of 14.7 so I switched it back.

[edcmat-l1]

One thing I've noticed is that when I am working on tuning my MAF, the problem is much worse. When I am working on VE, it's pretty much non existent.

As Alvin said you will probably run better in speed density. I'd say most of the time the GEN 3s will run better in speed density with moderate to bigger cams. Even more so for the Vettes.

With that cam you might get better results in SD mode.

I'm not sure I trust some of your guy's opinion about my wideband not being accurate. My wideband reading on VCM scanner matches my gauge readout...

But since I am open to trying new things, I am going to go out and do some tuning making corrections based off STFT's.

Here is my latest tune and its previous log using STFT's...
VE Tuning13 and MAF Step 12 changed stoich back to 14.7 throttle cracker put back to stock.hpt
VE12 Stoich at 14.7.hpl

I had my stoich afr set at 14.2 because I am in Cali runnning 91 octane, but I quickly observed that the O2 sensors have a calibration that is probably determining rich/lean based on the original tune of 14.7 so I switched it back.

It's ok you don't agree with my opinion about widebands being inaccurate. It was a general statement based on looking at a few thousand data logs over many years. Did not mean yours specifically. That being said you'll have better results tuning it in closed loop using your narrowband feedback and using your wideband for WOT only.

[WickedVetteZ06]

Just went through this issue on my 03 z06 (blower + blower cam), what fixed the issue for me was fixing a few different things.
-Set my base idle at 900 when car is warm
-Reenabled Rolling idle and set it to 950 across the board
-Tweaked my Idle Adaptive Spark control Underspeed table to look like this
underspeed spark.png

-Throttle Cracker Enable Speed set to 2, Disable set to 1
- My throttle Cracker Table looks like this
Throttle Cracker.png

-Rolling Idle Enable speed set to 2, Disable Speed set to 1
-Rolling Idle Airflow Adder, Copy the 1000RPM Column (closest RPM to your actual idle) from the Throttle Cracker and put those numbers into the Idle Airflow Adder Table, mine looks like this
Rolling Idle Airflow adder .png

-Adjusted throttle follower so the idle does not drop like a rock when clutching in and going into neutral, mine looks like this
Throttle Follower .png

Once I did these things, the low speed clutch-in stalling was fixed, and the idle dropping super low when going into neutral while rolling stopped as well. I'll attach my full tune also if you want to look at that.

[Alvin]

Just went through this issue on my 03 z06 (blower + blower cam), what fixed the issue for me was fixing a few different things.
-Set my base idle at 900 when car is warm
-Reenabled Rolling idle and set it to 950 across the board
-Tweaked my Idle Adaptive Spark control Underspeed table to look like this
underspeed spark.png

-Throttle Cracker Enable Speed set to 2, Disable set to 1
- My throttle Cracker Table looks like this
Throttle Cracker.png

-Rolling Idle Enable speed set to 2, Disable Speed set to 1
-Rolling Idle Airflow Adder, Copy the 1000RPM Column (closest RPM to your actual idle) from the Throttle Cracker and put those numbers into the Idle Airflow Adder Table, mine looks like this
Rolling Idle Airflow adder .png

-Adjusted throttle follower so the idle does not drop like a rock when clutching in and going into neutral, mine looks like this
Throttle Follower .png

Once I did these things, the low speed clutch-in stalling was fixed, and the idle dropping super low when going into neutral while rolling stopped as well. I'll attach my full tune also if you want to look at that.

I'm saying this respectfully.

When VE is dialed in very well. Injector data is good.. Almost none of these changes are needed.

[WickedVetteZ06]

I'm saying this respectfully.

When VE is dialed in very well. Injector data is good.. Almost none of these changes are needed.

I hear ya, Just figured I'd tell him what worked for me personally to get rid of the exact problem he is having with his car.

[G57]

I was having the same issue on my 05 Infiniti G35 w/ a LS1. RPMs would dip badly when shifting into neutral when coming to a stop and it would hunt for idle for a bit when revving it in neutral. Changed all values that @WickedVetteZ06 provided, and all is well now. Thanks!