2007 ly5 e38 super high idle, like scary high

have a 2007 ly5 with a fresh BTR cam (truck norris) and valvetrain, long tubes, otherwise stock.

Fighting an extremely high idle issue.

Engine started a few times, idle would hang around 1000 and idle would come down to about 750 after ~20 seconds, idled great, sounded great.


Now it starts and goes to 1800 rpm, starts to dip, then proceeds to go up to 3500+ rpm.

Commanded throttle SAE is like 27% during this, even after a throttle clean and commanding 10%, the PCM takes over an back to 27% it goes.

Have not found any vacuum leaks.

Any help is appreciated.

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Originally Posted by U W0t m8

have a 2007 ly5 with a fresh BTR cam (truck norris) and valvetrain, long tubes, otherwise stock.

Fighting an extremely high idle issue.

Engine started a few times, idle would hang around 1000 and idle would come down to about 750 after ~20 seconds, idled great, sounded great.


Now it starts and goes to 1800 rpm, starts to dip, then proceeds to go up to 3500+ rpm.

Commanded throttle SAE is like 27% during this, even after a throttle clean and commanding 10%, the PCM takes over an back to 27% it goes.

Have not found any vacuum leaks.

Any help is appreciated.

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You need to log more channels, especially commanded idle RPM. But it sounds to me like you have a massive vacuum leak.

And don't use SAE channels/pids on GM if you have other options for the throttle and accel pedal. They can be false values.

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Originally Posted by Cringer

You need to log more channels, especially commanded idle RPM. But it sounds to me like you have a massive vacuum leak.

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I added a few more channels and recorded some logs (before starting).

first log: sitting, doing nothing, then pressing the throttle to 100 a few times, Throttle position seems to be going crazy all on its own, constantly bouncing around, when not pressed to 100%.
second log: commanded the throttle position to 10% a few times, then 5% a few times, then 1% a few times. TPS always wants to be at 31% after I stop the commanded throttle, and it always higher than what i try to command it to.

Looks to me like i get to sit in my beautiful 110 degree Phoenix garage and bust out the volt meter, once i find the correct values and pinout for the TPS. I read another thread that said to disengage the TPS from the actuator, so i could manually control the throttle body once it starts. How bad of an idea is that?

I don't know what else i could do.

Additionally, i flashed a stock tune the other day just to see, and it does the same high idle thing.

Have you looked into RFI/EMI or trying to shield the throttle wires? Or tried a throttle relearn?

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Originally Posted by LS ROB

Have you looked into RFI/EMI or trying to shield the throttle wires? Or tried a throttle relearn?

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I have done the reset/relearn through vm scanner along with unplugging the battery multiple times.

Have not looked into any RF/EM interference at all. I can definitely buy some wrap for it, but I generally try not to throw parts at things. Ill have to look into inteference prevention options. I depinnied/repinned and reworked parts of the harness and maintained twist rates where applicable and tessa taped everything after, but that could be it.

I have not visually found any obvious areas where there is a vacuum leak, but i suppose its possible that the new manifold gasket was off enough to where it worked fine the first couple starts and then failed. I do have an idea I'm thinking about trying.

If I hook up a shop vac to suck air through a header and seal the intake, there shouod be a few valves open and theoretically if I put a smoke machine around the manifold, it could show me if there was a vacuum leak. Pretty off the wall thought, but that's where I'm at at unless a forum savior comes this way.

Engine is only throwing a coolant temp code, nothing related to air fuel throttle or spark.

Maybe I'm misunderstanding, but if you have a smoke machine, why don't you just blow the smoke in the intake directly? On the TBSS intake, you can pull off the evap tube and blow the smoke in there. No need to really seal the throttle body blade or anything because if it's that big of a vacuum leak, it should be pretty obvious. If it was small, then you need to seal the throttle blade.

Honestly your idle tables are a mess.

Is this still on an engine stand? (other thread)

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Originally Posted by cessnageek

Maybe I'm misunderstanding, but if you have a smoke machine, why don't you just blow the smoke in the intake directly? On the TBSS intake, you can pull off the evap tube and blow the smoke in there. No need to really seal the throttle body blade or anything because if it's that big of a vacuum leak, it should be pretty obvious. If it was small, then you need to seal the throttle blade.

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I don't have a smoke machine, yet. Was considering getting one.

I figured that the if I plugged the throttle body, and put a vacuum to the exhaust, I would very clear see if any smoke was entering via any other place but the throttle body.

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Originally Posted by 2xLS1

Is this still on an engine stand? (other thread)

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Yes, still on a stand. Every time I went to update that thread, it froze, so I made a new one.

I get that my idle tables are probably not great, which i will work on, once I can get the idle down. It's impossible (for me) to tune and make any adjustments right now without knowing the huge idle cause. I could start messing with tables and values, but the poke and learn method isn't worth blowing this motor up, since it goes to 4k rpm on cold start.

Since you looked over the tables, do you see anything that would expressly cause the idle to be so high?

You are wasting your time without and drivetrain load on the engine and full exhaust hooked up. But plug away.

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Originally Posted by 2xLS1

You are wasting your time without and drivetrain load on the engine and full exhaust hooked up. But plug away.

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It has a full exhaust hooked up

Learning is not a waste of time.

Thanks for your .02

Ok, well I would probably not do it that way if you get a smoke machine, just adds a lot of unnecessary complexity. FWIW I have a super cheap Amazon one that works really well for what I use it for. No need to spend the money on the snap on or whatever.

Also, it takes like 10 minutes to pull the intake off, especially if it's on an engine stand. So if you actually think that's where it's leaking, just take it off and reseat it.

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Originally Posted by cessnageek

Ok, well I would probably not do it that way if you get a smoke machine, just adds a lot of unnecessary complexity. FWIW I have a super cheap Amazon one that works really well for what I use it for. No need to spend the money on the snap on or whatever.

Also, it takes like 10 minutes to pull the intake off, especially if it's on an engine stand. So if you actually think that's where it's leaking, just take it off and reseat it.

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I'll have to take a look at the machines.

I don't have a clue where it could be leaking from. I know Cringer is very helpful around here and do believe if he didn't point out anything in the tune, and says it sounds like a leak, which it does for sure, that's probably what it is.

To be fair, its unbearably hot in my garage this time of year and it would be quicker to hook up the shop vac than it would to pull the intake, lol.

As there has been no input on the tune itself other than the above, which is not helpful is any sort, I'll focus on RF/EMI and look into vacuum leaks.

Thank you!

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Originally Posted by U W0t m8

I'll have to take a look at the machines.

I don't have a clue where it could be leaking from. I know Cringer is very helpful around here and do believe if he didn't point out anything in the tune, and says it sounds like a leak, which it does for sure, that's probably what it is.

To be fair, its unbearably hot in my garage this time of year and it would be quicker to hook up the shop vac than it would to pull the intake, lol.

As there has been no input on the tune itself other than the above, which is not helpful is any sort, I'll focus on RF/EMI and look into vacuum leaks.

Thank you!

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There are problems with the idle and other areas of the tune. Be that as it may, I don't see any reason why RPMs would climb to 3500 rpms. To me the only logical conclusion is vacuum leak, and that needs to be addressed before anymore tuning happens.

One more thought, if this is on an engine stand (without the load of the torque converter fighting a transmission in Park), then that may be part of the problem. You could try lowering the Min Final Airflow, and if that doesn't work work on the Torque Follower table....but then you are tuning around a problem that doesn't exist in the vehicle.

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Originally Posted by Cringer

One more thought, if this is on an engine stand (without the load of the torque converter fighting a transmission in Park), then that may be part of the problem. You could try lowering the Min Final Airflow, and if that doesn't work work on the Torque Follower table....but then you are tuning around a problem that doesn't exist in the vehicle.

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Thank you for the insight!

I bought a smoke machine, should be here in a couple days. I looked over everything again and nothing is obvious to the reason of a huge vacuum leak, but I hope the smoke machine will help with further diagnosis. And it's a new tool, so why not.

It is on a full running stand, but without the trans hooked up.

I don't have car for it yet, it's just a weekend project to play with. I have no doubt that it will act differently and tune differently when the load of the convertor is a factor. Just learning and playing, and struggling, that way once I can get a car to put it in, I'll at least know a little more.

Tuning around a problem that doesn't exist in a vehicle will be my foreseeable future, and I'm ok with it. Just trying to learn is all, but at the same time, definitely don't want it to break from how it's starting currently.

I'll adjust based on your recommendations, check for leaks, and report back.

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Originally Posted by Cringer

One more thought, if this is on an engine stand (without the load of the torque converter fighting a transmission in Park), then that may be part of the problem. You could try lowering the Min Final Airflow, and if that doesn't work work on the Torque Follower table....but then you are tuning around a problem that doesn't exist in the vehicle.

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So, kid went to bed early and this engine was on my mind, so i did some tests.

Did the shop-vac to the intake method, absolutely no air leaks found. Smoke machine still in route, but for now, i don't know if its an air leak, beacause..

It no longer has a high idle.

Now, it idles like absolute poo - in fact, it wont idle without throttle, and its doing a crazy surging/fluctuation (as seen in the log attached). It also puffing black smoke. BUT, no high idle, meaning..

It's a tune issue.

I adjusted base idle airflow, idle minimum, and 1% here and there in torque and rpm.

Now to figure out why the heck its jumping around so crazy!

Would hooking up the wideband be of any actual benefit at this point, or VVE/MAF tuning? Feel like idle needs to be sorted first, but now that its at least not gonna pop on startup, I'm curious.

Thank you for the recommendations so far!

Idle tuning is last