High Idle Log EFILive
Thread Starter
Joined: Nov 2003
Posts: 6,216
Likes: 236
From: Wichita KS / Rancho San Diego
High Idle Log EFILive If you have V7 EFILive, could you please check out this log file and give me any thoughts you may have about what could be happening? The backstory is in this thread: https://ls1tech.com/forums/pcm-diagn...e-control.html
in the log I'm cruising at about 40mph @ 1600 or so rpm with my foot off the throttle. As approach a stop, i shift into neutral to be able to slow down, (at about frame 25) and the rpms spike to about 2600, all with my foot off the throttle. As the car comes to rest, the idle slowly settles down to about 900 (setting is at 650).
This intermittent problem is continuing to vex me, and maybe someone who is a more expert tuner can see something in the log I don't see.
in the log I'm cruising at about 40mph @ 1600 or so rpm with my foot off the throttle. As approach a stop, i shift into neutral to be able to slow down, (at about frame 25) and the rpms spike to about 2600, all with my foot off the throttle. As the car comes to rest, the idle slowly settles down to about 900 (setting is at 650).
This intermittent problem is continuing to vex me, and maybe someone who is a more expert tuner can see something in the log I don't see.
Last edited by RevGTO; May 16, 2025 at 06:44 PM.
TECH Fanatic
Joined: Jan 2018
Posts: 1,059
Likes: 198
I don't have EFI Live, but what are your throttle-cracker and throttle-follower airflow values doing when this happens?
Also, I suspect that a vacuum leak could cause similar behavior, even if the tune was dialed in perfectly.
Also, I suspect that a vacuum leak could cause similar behavior, even if the tune was dialed in perfectly.
Thread Starter
Joined: Nov 2003
Posts: 6,216
Likes: 236
From: Wichita KS / Rancho San Diego
Vacuum leak was my first theory, but spray testing revealed nothing and likewise the smoke test that followed.
Throttle cracker varied between 0 and 0.32. Throttle follower was zero across the log.
Throttle cracker varied between 0 and 0.32. Throttle follower was zero across the log.
Last edited by RevGTO; May 16, 2025 at 11:05 PM.
Your IAC was about where it should be for a normal idle when it was well over 2000rpm. The IAC bottomed out completely closed just to get you below 900rpm. I have no idea where it is coming from, but you have an air leak somewhere. I ended up downloading EFI software just to look at your log. I must say, I am not a fan of their GUI.
Thread Starter
Joined: Nov 2003
Posts: 6,216
Likes: 236
From: Wichita KS / Rancho San Diego
Teching In
Joined: Dec 2024
Posts: 32
Likes: 0
From: Pa
If you have V7 EFILive, could you please check out this log file and give me any thoughts you may have about what could be happening? The backstory is in this thread: https://ls1tech.com/forums/pcm-diagn...e-control.html
in the log I'm cruising at about 40mph @ 1600 or so rpm with my foot off the throttle. As approach a stop, i shift into neutral to be able to slow down, (at about frame 25) and the rpms spike to about 2600, all with my foot off the throttle. As the car comes to rest, the idle slowly settles down to about 900 (setting is at 650).
This intermittent problem is continuing to vex me, and maybe someone who is a more expert tuner can see something in the log I don't see.
in the log I'm cruising at about 40mph @ 1600 or so rpm with my foot off the throttle. As approach a stop, i shift into neutral to be able to slow down, (at about frame 25) and the rpms spike to about 2600, all with my foot off the throttle. As the car comes to rest, the idle slowly settles down to about 900 (setting is at 650).
This intermittent problem is continuing to vex me, and maybe someone who is a more expert tuner can see something in the log I don't see.
Trending Topics
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo
His IAC completely closes, yet it has enough air to idle several hundred rpm higher than his set point. Unless the IAC reading is garbage, that is a mechanical issue. And yes, having a bad IAC reading is possible, but it is obviously moving, so???
Thread Starter
Joined: Nov 2003
Posts: 6,216
Likes: 236
From: Wichita KS / Rancho San Diego
Joined: Nov 2001
Posts: 34,628
Likes: 2,543
From: Schiller Park, ILL Member: #317
I don't think it's tune related either.
@RevGTO, I can't recall, did you ever replace your EVAP purge solenoid? Going back to our posts in the other thread, this was the answer to my (similar) problem for many years until it recently came back, but in a slightly different and more minor way (and I now think that the reemergence was likely a new/different issue related to the battery/battery cables). If the purge solenoid was occasionally opening more than commanded (or hanging open until engine restart), you would never expose this with any sort of smoke test or other vacuum leak check, as it wouldn't be a fixed leak that could be detected with the engine off. And that's what seemed to be the case for my (original) issue as well - all signs pointed to a vacuum leak, other than the fact that the issue could be cleared with a restart of the engine and no external leak source could ever be found.
Even if you look at EVAP duty cycle, all that tells you is what the PCM has commanded; there is no feedback loop to let you know how far open the solenoid actually is. So if it's sometimes hanging open more than it should be (for given conditions and PCM commands), the result will be excess air fed into the engine that is outside the control of the IAC motor and won't ever be detectable with a smoke machine.
@RevGTO, I can't recall, did you ever replace your EVAP purge solenoid? Going back to our posts in the other thread, this was the answer to my (similar) problem for many years until it recently came back, but in a slightly different and more minor way (and I now think that the reemergence was likely a new/different issue related to the battery/battery cables). If the purge solenoid was occasionally opening more than commanded (or hanging open until engine restart), you would never expose this with any sort of smoke test or other vacuum leak check, as it wouldn't be a fixed leak that could be detected with the engine off. And that's what seemed to be the case for my (original) issue as well - all signs pointed to a vacuum leak, other than the fact that the issue could be cleared with a restart of the engine and no external leak source could ever be found.
Even if you look at EVAP duty cycle, all that tells you is what the PCM has commanded; there is no feedback loop to let you know how far open the solenoid actually is. So if it's sometimes hanging open more than it should be (for given conditions and PCM commands), the result will be excess air fed into the engine that is outside the control of the IAC motor and won't ever be detectable with a smoke machine.
Thread Starter
Joined: Nov 2003
Posts: 6,216
Likes: 236
From: Wichita KS / Rancho San Diego
I don't think it's tune related either.
@RevGTO, I can't recall, did you ever replace your EVAP purge solenoid? If it's sometimes hanging open more than it should be (for given conditions and PCM commands), the result will be excess air fed into the engine that is outside the control of the IAC motor and won't ever be detectable with a smoke machine.
@RevGTO, I can't recall, did you ever replace your EVAP purge solenoid? If it's sometimes hanging open more than it should be (for given conditions and PCM commands), the result will be excess air fed into the engine that is outside the control of the IAC motor and won't ever be detectable with a smoke machine.
It seems like over the course of the other thread you checked everything that can be safely checked. This leads me to speculate again about the brake booster or hose going to it. However, the only way I can think to hope to recreate the problem and check for this without killing people involves a lot of dyno time. Probably both cost and time prohibitive to check in that manner.
Joined: Nov 2001
Posts: 34,628
Likes: 2,543
From: Schiller Park, ILL Member: #317
I've dealt with failed (and failing) brake boosters before, ranging from catastrophic failure to just a slight leak. It's pretty easy to rule this out by simply checking for any remaining power assist after engine shutdown. If you still have power assist (vacuum) remaining in the booster after several hours (or days), then it's certainly not leaking. And I've never had one intermittently leak - it's just a rubber diaphragm that's either leaking or isn't.
In fact, the brake booster in my wife's car (2012 Malibu) has a very minor leak currently, and will lose power assist about 5 minutes after engine shutdown (our other same-gen Malibu will hold power assist for days), but it's not enough of a leak to cause any driveability issues. IMO, if the booster holds vacuum for more than 5 minutes after engine shutdown, any leak there wouldn't be big enough to cause RevGTO's idle hang issues, and if it holds vacuum for hours or days after shutdown then it's definitely not the cause. On the other hand, if vacuum dissipates immediately upon shutdown then it's certainly a possibility or at least a contributing factor.
In fact, the brake booster in my wife's car (2012 Malibu) has a very minor leak currently, and will lose power assist about 5 minutes after engine shutdown (our other same-gen Malibu will hold power assist for days), but it's not enough of a leak to cause any driveability issues. IMO, if the booster holds vacuum for more than 5 minutes after engine shutdown, any leak there wouldn't be big enough to cause RevGTO's idle hang issues, and if it holds vacuum for hours or days after shutdown then it's definitely not the cause. On the other hand, if vacuum dissipates immediately upon shutdown then it's certainly a possibility or at least a contributing factor.
Disregard what I said earlier — I made a rookie mistake. I installed EFILive on this PC, opened a log, and started playing it back. I was hitting "Stop" thinking it would pause the log so I could review data, but it turns out "Stop" actually halts playback and resets the data view, which led to some confusion. I haven’t used EFILive since around 2014 and don’t have it set up on any of my current systems, so I’m definitely a bit rusty after a decade away from it.