RPMs rise and hold at ~2200 unless I'm stopped.

[JakeRobb]

Whenever I'm driving around, my RPMs tend toward 2200 unless I'm giving it throttle or if the engine speed is pulling it down. Coasting, cruising, whatever. Cruise set at 40 in 5th gear and it will accelerate to 50 or so all by itself. Slow the car down in gear using the brakes and the revs will come down, but they'll rise again if I press the clutch, shift to neutral, or let go of the brakes.

At first I thought I had a massive air leak, but if I come to a complete stop (or a suuuper slow crawl -- anything that registers as 0mph in the PCM), it settles down to a normal idle, so I think it has to be a software thing. Engine is at operating temp and IAC is at 0 when this happens.

Anybody seen this before?

Tune file: jakerobb.hpt

Log file: 24-07-18 19-53-27.hpl

EDIT: now that I'm actually looking at the log, I can see that IAC is not at zero like I thought, but is going wild -- counts ranging well over 200. What causes that?

[Markolc81]

I'll take some stabs here.

First, I assume you have no MAF sensor

What injectors?

Your VE table looks like it will poke my eyes out. Some incredible peaks and valleys there. I'd upload a stock one and start over.

According to your log, you are super super lean, especially in Bank 2 O2 sensor throughout out most of the log.. I would double check you don't have an exhaust leak before the O2 sensor on that side. Also double check your O2 sensors are on the correct sides.

Lean condition would cause the motor to surge at light throttles.

Your IAC is just trying to make sense of the information given

[JakeRobb]

Thanks very much for the reply!!

I assume you have no MAF sensor

I have a MAF sensor, but it's not calibrated yet. It's disabled right now while I figure out VE stuff. (This is the approach that was suggested to me by others here; if you think it's a mistake, I'd love to know more!)

What injectors?

I forget the P/N, but they're from a stock LS3. Got the injector data from a spreadsheet that gets passed around here.

Your VE table looks like it will poke my eyes out. Some incredible peaks and valleys there. I'd upload a stock one and start over.

That tracks. I'm still learning; this is my first time tuning anything. I know that one of the things I still need to learn to do is apply smoothing. Another is to look at the VE graph and understand what it's telling me.

According to your log, you are super super lean, especially in Bank 2 O2 sensor throughout out most of the log. I would double check you don't have an exhaust leak before the O2 sensor on that side. Also double check your O2 sensors are on the correct sides.

Okay, I will inspect. Given the layout of the factory engine harness, I don?t think it's possible for them to be on the wrong side.

My wideband is on bank 1 (and you can see what it's saying via the EGR input), if that tells you anything.

Lean condition would cause the motor to surge at light throttles.

Interesting. Can you explain why that is?

Your IAC is just trying to make sense of the information given

I suppose that makes sense given the other issues. Can you tell me what inputs/conditions control IAC behavior?

[Markolc81]

No issues tuning your VE first, don't need your MAF for this, I'm just confirming because I saw no MAF curve. But you do have it disabled, so no issues there.

You are going to have to decide if you will tune your part throttle using a wideband, or the stock O2 sensors. The log you provided above shows the motor as running Lean, and your stock O2s are commanding the PCM to compensate with more fuel. Your Wideband is reading the corrected fuel data, which should be around stoich, anywhere in part throttle.

There is one point in your log where you climb just past 4k RPM, and you enter Open Loop, likely Power Enrichment, and your Wideband pegs at 5v. Not sure if that's full rich or full lean on your wideband, but pegging the sensor to either extreme is not likely what you're looking for. But you are also in a transient state, so it's hard to put much stock into that reading.

If you choose to tune your part throttle with a wideband, You would need to set up math to convert your voltage to lambda for your specific wideband, and then you can log the lambda vs desired lambda and figure out the error percentage. There are some great tutorials on how to do this on Youtube and buried on this forum.

If you choose to tune your part throttle with the stock O2s, then a lot of the charts are already present there for you, you may need to tweak slightly.

Either way, reset your VE table to the stock one and start over. Reset your LTFTs, and run another short log of driving. If you're still super lean on one bank, then look for an exhaust leak.

Your biggest issue with drivability according to the log, is that you are running lean, and significantly so on Bank 2. Any misfires on cyl 2,4,6,8? Down a cylinder? If you disable one injector at a time using the VCM Scanner, (2,4,6,8 cylinders) does the motor run the same or worse? If you are for sure firing on all 8, then I'd investigate a possible exhaust leak before the sensor on Bank 2.

[edcmat-l1]

Jakerobb VE.jpg

First off, you can't have a VE that looks like this.

Second, you need to search how to setup your IAC and TPS. The IAC counts when at operating temp should be 40-60. And your TPS percentage needs to be zero. You have to either adjust the throttle blade opening or drill a larger hole in the blade to get the counts down while keeping your TPS voltage around .5v.

Once you get the IAC setup correctly it will cure most of your idle issues, once the VE is corrected.

[JakeRobb]

You are going to have to decide if you will tune your part throttle using a wideband, or the stock O2 sensors. The log you provided above shows the motor as running Lean, and your stock O2s are commanding the PCM to compensate with more fuel. Your Wideband is reading the corrected fuel data, which should be around stoich, anywhere in part throttle.

The wideband is there for WOT/PE tuning. I just think it's a useful double-check on the possible lean condition. I want to be able to run in closed loop with everything running more or less how it did from the factory.

There is one point in your log where you climb just past 4k RPM, and you enter Open Loop, likely Power Enrichment, and your Wideband pegs at 5v. Not sure if that's full rich or full lean on your wideband, but pegging the sensor to either extreme is not likely what you're looking for. But you are also in a transient state, so it's hard to put much stock into that reading.

The paperwork that came with the wideband says it scales linearly between 0v=10:1 and 5v=20:1, so that'd be full lean. I haven't done any PE tuning at all yet (just got the wideband hooked up recently) and have mostly been avoiding >4krpm for that reason.

If you choose to tune your part throttle with a wideband, You would need to set up math to convert your voltage to lambda for your specific wideband, and then you can log the lambda vs desired lambda and figure out the error percentage. There are some great tutorials on how to do this on Youtube and buried on this forum.

I have the math set up on my end. I thought that my configuration was included with the HPL file, but I guess not. Should I share my config file as well in the future?

Either way, reset your VE table to the stock one and start over. Reset your LTFTs, and run another short log of driving. If you're still super lean on one bank, then look for an exhaust leak.

Your biggest issue with drivability according to the log, is that you are running lean, and significantly so on Bank 2. Any misfires on cyl 2,4,6,8? Down a cylinder? If you disable one injector at a time using the VCM Scanner, (2,4,6,8 cylinders) does the motor run the same or worse? If you are for sure firing on all 8, then I'd investigate a possible exhaust leak before the sensor on Bank 2.

I'll give all this a shot. Thanks!

[JakeRobb]

The IAC counts when at operating temp should be 40-60.

Okay, that's good to know. Thanks. Seems to be falling to zero as it is, which for some reason I thought was normal.

And your TPS percentage needs to be zero. You have to either adjust the throttle blade opening or drill a larger hole in the blade to get the counts down while keeping your TPS voltage around .5v.

Ah, shoot. I had that working (TPS 0%), but then it kept dying at idle so I turned the throttle stop screw a tiny bit. Totally forgot that would affect the TPS minimum. I'll set the stop screw back where it was and figure out the IAC stuff.

Once you get the IAC setup correctly it will cure most of your idle issues, once the VE is corrected.

Thanks!

[JakeRobb]

Haven't had time to come back to this, but I've realized something.

I don't deny that my VE table is all messed up, nor that I need my TPS to read 0v.

But I still wonder -- why does this high-idle behavior go away completely when I'm stopped? If the car isn't moving, the idle is much closer to normal. (See ~07:40 in the log for an example.)

[edcmat-l1]

Because when the PCM sees zero VSS your idle controls kick in. LTIT, STIT (air) and timing work together to get it to idle, and to maintain idle.

Stop second guessing and go through the procedure I laid out. This is the procedure for setting up a cable throttle body. It's not just "getting your TPS to zero" it's getting your IAC counts to 40-60 at operating temp that is the key.

[JakeRobb]

Because when the PCM sees zero VSS your idle controls kick in. LTIT, STIT (air) and timing work together to get it to idle, and to maintain idle.

I assume LTIT/STIT are Long/Short Term Idle Trims, and that they work similarly to fuel trims. What are they trimming, exactly? At a glance through things I can see in Scanner, it doesn't seem like they're trimming fuel.

Not sure what "(air)" is clarifying here, but it probably has something to do with the fact that I don't see STIT in the params list.

I see in the param selector that there are LTIT tables for Gear and Park/Neutral. My car is a manual, and AFAIK the PCM doesn't know which I'm in. I know it can tell when the clutch pedal is depressed, but I'm 99% sure there's no signal telling it whether the gear lever is in neutral. Does it just always use the Gear tables?

Stop second guessing and go through the procedure I laid out. This is the procedure for setting up a cable throttle body. It's not just "getting your TPS to zero" it's getting your IAC counts to 40-60 at operating temp that is the key.

Don't worry, I'm not second guessing. Just trying to learn how things work. I'm not the kind of guy that will be satisfied with a car that's running right. I like to understand how things work so that I can apply those lessons later on.

I haven't touched the car since posting this topic. When I do, I plan to follow your procedure.

[gtstorey]

I'm not the kind of guy that will be satisfied with a car that's running right. I like to understand how things work so that I can apply those lessons later on.

There will always be a limit to understanding things in the tuning world. It varies with the ECM but there are always a lot more tables within the ecm that are undefined than defined. And some of this will become more clear as you do it vs. someone writing you a book to explain it.

[bk2life]

any updates?

[JakeRobb]

any updates?

Not really. I made some progress, but also hit some more hurdles.

My cheap Speed Engineering throttle body seems to be the source of many of my problems. I was half-expecting this (though I had high hopes since it uses OEM GM sensors). I'm seeing TPS voltage circle back around to zero at somewhere around 70% throttle, and I'm also having a ton of trouble getting a reliable 0% -- I'll adjust the stop, do the reset, see 0%, then as soon as I touch the pedal it won't go below 0.4% anymore. I also wasn't happy with the throttle tip-in behavior, though that might have been a tuning thing. I have not yet ordered something better for budget reasons. Planning on a NW 92mm. I should be able to order it later this week.

I'm also currently sidetracked by a leaky brake fitting that's preventing me from doing more driving and datalogging. Haven't fixed it because it's been insanely hot lately and we've been spending all our free time at the in-law's lake house rather than in the garage.

Before the brake leak appeared, I went through some of the steps prescribed and did some more driving and logging. I'm pretty happy with the progress I've made on the VE tables (so long as I don't go past that 70% threshold and confuse everything), but there's still a good way to go.

I haven't tried dialing in the IAC yet; didn't get far enough with TPS reliability before I decided to bail and get the NW. Haven't even searched for a good how-to yet. If you happen to know of a particularly good guide for someone who's never done it before, I'd appreciate a link.

[edcmat-l1]

.4% throttle at idle is OK. A lot of them end up at that exact number. It still considers that idle. You can tell because the over/under speed spark works.

BTW I've done a bunch of GN tuning over the years including quite a bit of FAST XFI setups. I've been a FAST dealer for close to 20 years. If you ever need any help let me know.

[bk2life]

I haven't tried dialing in the IAC yet. If you happen to know of a particularly good guide for someone who's never done it before, I'd appreciate a link.

a how to for the IAC?
im learning myself like right now, i posted a thread almost above yours.

But seems you adjust the throttle black to get the IACs don around 60, and then adjust the tps to keep the voltage down (i dont have the exact number in front of me) and then turn key off remove the TPS plug, turn key on let ist for 20 seconds. Turn key off, plug in the TPS and you should be ready for the next round of datalogging.

[gtstorey]

Iac setup
https://www.pcmofnc.com/2021/03/05/i...throttle-body/

[JakeRobb]

.4% throttle at idle is OK. A lot of them end up at that exact number. It still considers that idle.

I'm inclined to believe you, but the setup guide gstorey posted above says 0.00%. Is the tolerance something that's configured somewhere in the tune file? Does it vary by PCM model or OS?

You can tell because the over/under speed spark works.

You can tell. I probably could if I knew how or where to look for that. (I haven't gotten into spark tuning at all yet; just going with stock LS1 stuff so far and focusing on fueling.)

FWIW, I was seeing difficulty maintaining idle when it was showing 0.4%. Could be because I haven't done the IAC stuff yet though...

BTW I've done a bunch of GN tuning over the years including quite a bit of FAST XFI setups. I've been a FAST dealer for close to 20 years. If you ever need any help let me know.

Thanks, but it was professionally tuned. I believe we're in good shape there. That said, the tuner has since gone out of business (owner passed away), so if we ever need to revisit the tune after further modifications, I'll keep this in mind. Thanks!

But seems you adjust the throttle black to get the IACs don around 60

I have to assume "throttle black" is some kind of typo. Throttle blade? If this is what you mean, I'd advise that you read the link gstorey posted, because it explicitly says not to adjust your IACs that way, and gives clear reasons why it's not a good idea.

Iac setup
https://www.pcmofnc.com/2021/03/05/i...throttle-body/

Thanks! One thing it says in there:

1. The engine should be tuned decently well. Too rich or lean will greatly effect this adjustment. We often save this adjustment until the fuel trims are +/- 10% and the wideband is reading near stoich

Can we define "near stoich"? I'm using lambda. Some searching shows that I should target a range of .98-1.02. Anybody disagree?

While we're on the subject of my wideband readings, I just want to check something. My datalogs always have big lean spikes (sensor maxes out) when I shift (here's where I remind you all it's a manual transmission ). This feels backward to me -- closing the throttle suddenly should create a shortage of air, and should result in a rich condition until the PCM can react and the results can reach the wideband. Unless the system is fast enough to notice the closed throttle and cut fuel within a single combustion event, but there's still air in the intake manifold... yeah. I could theorize all day long, but I'm hoping someone here can clear this up.

[ns158sl]

IAC should dam near be maxxed when applying the accelerator. Your RAF or follower/cracker might be affecting. Never looked at the log yet. Listen to Ed.

[JakeRobb]

IAC should dam near be maxxed when applying the accelerator.

Maxed as in counts well over 200? That's surprising to me; why? Upon consideration, my guess is so that there's enough air flowing through the throttle that it can "catch" itself when I stop accelerating and the RPMs fall, so that it can return to a controlled idle rather than stalling. Then as RPMs approach the idle target, it can start dialing it back to the desired 50-60 range to get things under control.

I haven't paid attention to IAC when not at idle, so I have no idea whether this is the case at the moment.

Your RAF or follower/cracker might be affecting.

This is the first time I'm encountering any of those terms. I searched and found that RAF is Running Air Flow, and found some tidbits about follower and cracker, but still feel like I have no idea what their purposes are, nor whether/how I can/should adjust them. Any additional explanation would be appreciated!

I'm pretty sure I'm not even logging them; what should I be looking for?

EDIT: did more reading on follower and cracker. I think I'm starting to get it.

[twenglish1]

To add to what everyone else has been saying after getting the idle air figured out you will also want to make sure all your spark advance tables, high and low octane and the idle park/neutral and idle in gear spark tables all kinda "mesh" nicely together, you want your idle table to lead into your main spark tables to make the transition is as smooth as possible